Methods of identifying compounds that target trna splicing endonuclease and uses of said compounds as anti-proliferative agents

ABSTRACT

The present invention relates to a method for screening and identifying compounds that modulate the activity tRNA splicing endonuclease. In particular, the invention provides assays for the identification of compounds that inhibit animalia tRNA splicing endonuclease. The methods of the present invention provide a simple, sensitive assay for high-throughput screening of libraries of compounds to identify pharmaceutical leads useful for treating and/or preventing cancer.

1. INTRODUCTION

The present invention relates to a method for screening and identifyingcompounds that modulate the activity of an animialia tRNA splicingendonuclease. In particular, the invention provides assays for theidentification of compounds that inhibit or reduce the activity of ananimalia tRNA splicing endonuclease. The methods of the presentinvention provide a simple, sensitive assay for high-throughputscreening of libraries of compounds to identify pharmaceutical leadsuseful for preventing, treating, managing or ameliorating cancer or oneor more symptoms thereof.

2. BACKGROUND OF THE INVENTION

2.1 Cancer and Neoplastic Disease

Cancer is the second leading cause of death in the United States. TheAmerican Cancer Society estimated that in 2001, there would be 1.3million new cases of cancer and that cancer will cause 550,000 deaths.Overall rates have declined by 1% per year during the 1990s. There are 9million Americans alive who have ever had cancer. NIH estimates thedirect medical costs of cancer as $60 billion.

Currently, cancer therapy involves surgery, chemotherapy and/orradiation treatment to eradicate neoplastic cells in a patient (see, forexample, Stockdale, 1998, “Principles of Cancer Patient Management”, inScientific American: Medicine, vol. 3, Rubenstein and Federman, eds.,Chapter 12, Section IV). All of these approaches pose significantdrawbacks for the patient. Surgery, for example, can be contraindicateddue to the health of the patient or can be unacceptable to the patient.Additionally, surgery might not completely remove the neoplastic tissue.Radiation therapy is effective only when the irradiated neoplastictissue exhibits a higher sensitivity to radiation than normal tissue,and radiation therapy can also often elicit serious side effects. (Id.)With respect to chemotherapy, there are a variety of chemotherapeuticagents available for treatment of neoplastic disease. However, despitethe availability of a variety of chemotherapeutic agents, traditionalchemotherapy has many drawbacks (see, for example, Stockdale, 1998,“Principles Of Cancer Patient Management” in Scientific AmericanMedicine, vol. 3, Rubenstein and Federman, eds., ch. 12, sect. 10).Almost all chemotherapeutic agents are toxic, and chemotherapy can causesignificant, and often dangerous, side effects, including severe nausea,bone marrow depression, immunosuppression, etc. Additionally, many tumorcells are resistant or develop resistance to chemotherapeutic agentsthrough multi-drug resistance.

Therefore, there is a significant need in the art for novel compoundsand compositions, and methods that are useful for treating cancer orneoplastic disease with reduced or without the aforementioned sideeffects. Further, there is a need for cancer treatments that providecancer-cell-specific therapies with increased specificity and decreasedtoxicity.

2.2 tRNA Production

Maturation and maintenance of tRNA within eucaryal cells requiresseveral processing events including 5′ and 3′ end-trimming, modificationof specific bases and in some cases, intron removal. The enzymes forthese various steps in processing have been characterized in the yeast,archaeal, mammalian and bacterial systems (Deutscher, M. P. tRNAProcessing Nucleases, in tRNA:Structure, Biosynthesis and Function, D.Soll and U. RjaBhandary (eds.), American Society for Microbiology,Washington D.C., (1995), pp. 51-65). 5′ end trimming requires theactivity of Rnase P and 3′ end trimming requires the function of variousendo- and exo-nucleases. Modification occurs through interaction of tRNAwith various modification enzymes. Most tRNAs contain a number of globalas well as, species-specific modifications (Bjork, G. Biosynthesis andFunction of Modified Nucleosides, in tRNA: Structure, Biosynthesis andFunction, D. Soll and U. RajBhandary (eds.), American Society forMicrobiology, Washington D.C., (1995), pp. 165-205). In archaea andeucarya, several isoaccepting groups of tRNA contain interveningsequences ranging in size from 14-105 nucleotides (Trotta, C. R. andAbelson, J. N. tRNA Splicing: An RNA World Add-On or an AncientReaction? In RNA World II, Tom Cech, Ray Gesteland and John Atkins(eds.), Cold Spring Harbor Laboratory Press (1999) and Abelson et al.,1998, Journal of Biological Chemistry 273:12685-12688). Removal of theintron requires the activity of 3 enzymes. In the first step, the tRNAis recognized and cleaved at the 5′ and 3′ junction by the tRNA splicingendonuclease. The archaeal and eucaryal tRNA endonuclease areevolutionary conserved enzymes and contain a similar active site toachieve cleavage at the 5′ and 3′ splice sites. However, they havediverged to recognize the tRNA substrate in a different manner. Thearchaeal enzyme recognizes a conserved intronic structure known as thebulge-helix-bulge. This structure is comprised of two 3-nucleotidebulges separated by a 4-nucleotide helix. Cleavage occurs within eachbulge to release the intron. The eucaryal endonuclease recognizes thetRNA substrate in a mature domain dependent fashion, measuring a setdistance from the mature domain to the 5′ and 3′ splice sites (Reyes etal., 1988, Cell 55:719-730). It has recently been demonstrated, however,that the eucaryal enzyme requires a bulge at each splice site and thatthe enzyme has actually retained the ability to recognize tRNA by anintron-dependent recognition mechanism identical to that of the archaealendonuclease (Fruscoloni et al., 2001, EMBO Rep 2:217-221). Oncecleaved, the tRNA half molecules are ligated by the action of a uniquetRNA splicing ligase (Trotta, C. R. and Abelson, J. N. tRNA Splicing: AnRNA World Add-On or an Ancient Reaction? In RNA World II, Tom Cech, RayGesteland and John Atkins (eds.), Cold Spring Harbor Laboratory Press(1999) and Abelson et al., 1998, Journal of Biological Chemistry273:12685-12688). In yeast, the product of ligation is a tRNA with aphosphate at the splice junction. Removal of the phosphate is carriedout by a tRNA 2′-phosphotransferase to yield a mature tRNA product(Trotta, C. R. and Abelson, J. N. tRNA Splicing: An RNA World Add-On oran Ancient Reaction? In RNA World II, Tom Cech, Ray Gesteland and JohnAtkins (eds.), Cold Spring Harbor Laboratory Press (1999) and Abelson etal., 1998, Journal of Biological Chemistry 273:12685-12688).

tRNA is an important component in the translational machinery and isquite stable compared to various other protein-based components(elongation factors, amino-acyl synthetases, etc.). tRNA molecules havevery long half-lives. Furthermore, like rRNA and ribosomes, tRNA ispresent in excess within the cytoplasm of actively growing cells(Ikemura, T. and Okeki, H., 1983, Cold Spring Harbor Symp. Quant. Biol.47:1087-1097). Thus, specific targeting of tRNA molecules allows aselective inhibition of uncontrolled cell proliferation and not cellgrowth.

Citation of any of the reference herein is not to be construed as anadmission of its availability as prior art.

3. SUMMARY OF THE INVENTION

The present invention provides methods for identifying a compound thatmodulates the activity of an animalia tRNA splicing endonuclease. Inparticular, the invention provides methods for identifying a compoundthat inhibits the activity of an animalia tRNA splicing endonuclease.The invention encompasses the use of the compounds identified utilizingthe methods of the invention for the prevention, treatment, managementor amelioration of a proliferative disorder or a symptom thereof.

The invention provides cell-based and cell-free assays for theidentification of a compound that modulates the activity of an animaliatRNA splicing endonuclease, preferably a mammalian tRNA splicingendonuclease and most preferably a human tRNA splicing endonuclease.These assays may be reporter gene-based assays, fluorescence resonanceenergy transfer (“FRET”)-based assays, or fluorescence polarizationassays and may be conducted in a high throughput screen format. Further,these assays directly or indirectly measure the ability of a compound tomodulate an animalia tRNA splicing endonuclease. In a preferredembodiment, the ability of a compound to modulate animalia tRNA splicingendonuclease activity that was identified utilizing an indirect assay(e.g., a cell-based assay such as a reporter gene cell-based assay or aFRET cell-based assay) is confirmed utilizing a more direct assay (e.g.a FISH assay).

The reporter gene-based assays may be conducted by contacting a compoundwith an animalia cell genetically engineered to express a nucleic acidcomprising a reporter gene, wherein the reporter gene comprises a tRNAintron, and measuring the expression of said reporter gene.Alternatively, the reporter gene-based assays may be conducted bycontacting a compound with an animalia cell-free extract and a nucleicacid comprising a reporter gene, wherein the reporter gene comprises atRNA intron, and measuring the expression of said reporter gene. Thealteration in reporter gene expression relative to a previouslydetermined reference range, or to the expression in the absence of thecompound or the presence of an appropriate control (e.g., a negativecontrol) in such reporter-gene based assays indicates that a particularcompound modulates the activity of the tRNA splicing endonuclease. Inparticular, a decrease in reporter gene expression relative to apreviously determined reference range, or to the expression in theabsence of the compound or the presence of an appropriate control (e.g.,a negative control) in such reporter-gene based assays indicates that aparticular compound reduces or inhibits the activity of an animalia tRNAsplicing endonuclease (e.g. the recognition or cleavage of a tRNAintron). In contrast, an increase in reporter gene expression relativeto a previously determined reference range, or to the expression in theabsence of the compound or the presence of an appropriate control (e.g.,a negative control) in such reporter-gene based assays indicates that aparticular compound enhances the activity of an animalia tRNA splicingendonuclease.

In one embodiment, the invention provides a method for identifying acompound that modulates animalia tRNA splicing endonuclease activity,said method comprising: (a) expressing a nucleic acid comprising areporter gene in a cell, wherein the reporter gene comprises a tRNAintron; (b) contacting said cell with a member of a library ofcompounds; and (c) detecting the expression of said reporter gene,wherein a compound that modulates tRNA splicing endonuclease activity isidentified if the expression of said reporter gene in the presence of acompound is altered relative to a previously determined reference range,or the expression of said reporter gene in the absence of the compoundor the presence of an appropriate control (e.g., a negative control).

In another embodiment, the invention provides a method for identifying acompound that modulates animalia tRNA splicing endonuclease activity,said method comprising: (a) contacting a member of a library ofcompounds with a cell containing a nucleic acid comprising a reportergene, wherein the reporter gene comprises a tRNA intron; and (b)detecting the expression of said reporter gene, wherein a compound thatmodulates tRNA splicing endonuclease activity is identified if theexpression of said reporter gene in the presence of a compound isaltered relative to a previously determined reference range, or theexpression of said reporter gene in the absence of said compound or thepresence of an appropriate control (e.g., a negative control).

In another embodiment, the invention provides a method for identifying acompound that modulates animalia tRNA splicing endonuclease activity,said method comprising: (a) contacting a member of a library ofcompounds with a cell-free extract and a nucleic acid comprising areporter gene, wherein the reporter gene comprises a tRNA intron; and(b) detecting the expression of said reporter gene, wherein a compoundthat modulates tRNA splicing endonuclease activity is identified if theexpression of said reporter gene in the presence of a compound isaltered relative to a previously determined reference range, or theexpression of said reporter gene in the absence of said compound or thepresence of an appropriate control (e.g., a negative control).

In accordance with the invention, the step of contacting a compound witha cell, or cell-free extract and a nucleic acid in the reportergene-based assays described herein is preferably conducted in an aqueoussolution comprising a buffer and a combination of salts (such as KCl,NaCl and/or MgCl₂). The optimal concentration of each salt used in theaqueous solution is dependent on the endonuclease and the compoundsused, and can be determined using routine experimentation. In a specificembodiment, the aqueous solution approximates or mimics physiologicconditions. In another specific embodiment, the aqueous solution furthercomprises a detergent or a surfactant.

The reporter gene constructs utilized in the reporter gene-based assaysdescribed herein may comprise the coding region of a reporter gene and atRNA intron that renders the mRNA coding the reporter gene out of frame.Alternatively, the reporter gene constructs utilized in the reportergene-based assays described herein comprise a tRNA intron within the 5′untranslated region, 3′ untranslated region or both the 5′ and 3′untranslated regions. In another alternative, the tRNA intron interruptsan mRNA splicing element. In a specific embodiment, a reporter geneconstruct utilized in the reporter gene-based assays described hereincomprises the coding region of a reporter gene and a tRNA intron withinthe open reading frame of the reporter gene. The intron utilized in thereporter gene constructs described herein may comprise abulge-helix-bulge conformation. In a preferred embodiment, a reportergene construct utilized in the reporter-gene-based assays describedherein comprises a mature domain containing a tRNA intron.

Any reporter gene well-known to one of skill in the art may be utilizedin the reporter gene constructs described herein. Examples of reportergenes include, but are not limited to, the gene encoding fireflyluciferase, the gene coding renilla luciferase, the gene encoding clickbeetle luciferase, the gene encoding green fluorescent protein, the geneencoding yellow fluorescent protein, the gene encoding red fluorescentprotein, the gene encoding cyan fluorescent protein, the gene encodingblue fluorescent protein, the gene encoding beta-galactosidase, the geneencoding beta-glucoronidase, the gene encoding beta-lactamase, the geneencoding chloramphenicol acetyltransferase, and the gene encodingalkaline phosphatase.

The reporter gene-based assays described herein may be conducted in acell genetically engineered to express a reporter gene or in vitroutilizing a cell-free extract. Any cell or cell line of any specieswell-known to one of skill in the art may be utilized in accordance withthe methods of the invention. Further, a cell-free extract may bederived from any cell or cell line of any species well-known to one ofskill in the art. Examples of cells and cell types include, but are notlimited to, human cells, cultured mouse cells, cultured rat cells orChinese hamster ovary (“CHO”) cells.

Fluoroscent resonance energy transfer (“FRET”) assays may be used toidentify a compound that modulates the activity of an animalia tRNAsplicing endonuclease. The FRET assays may be conducted utilizinglabeled subunits of an animalia tRNA splicing endonuclease or labeledsubstrates for an animalia tRNA splicing endonuclease. The FRETcell-based assays may be conducted by microinjecting or transfecting asubstrate for an animalia tRNA splicing endonuclease into an animaliacell and contacting the cell with a compound, wherein the substrate islabeled at the 5′ end with a fluorophore and labeled at the 3′ end witha quencher, or, alternatively, the substrate is labeled at the 5′ endwith a quencher and labeled at the 3′ end with a fluorophore, andmeasuring the fluorescence of the substrate by, e.g., fluorescencemicroscopy or a fluorescence emission detector such as a Viewlux orAnalyst. The endogenous tRNA splicing endonuclease will cleave thesubstrate and result in the production of a detectable fluorescentsignal. A compound that inhibits or reduces the activity of theendogenous tRNA splicing endonuclease will inhibit or reduce thecleavage of the substrate and thus, inhibit or reduce the production ofa detectable fluorescent signal. A compound that enhances the activityof the endogenous endonuclease will enhance the cleavage of thesubstrate and thus, increase the production of a detectable fluoroscentsignal. Alternatively, the FRET cell-based assays may be conducted bymicroinjecting or transfecting a substrate for an animalia tRNA splicingendonuclease into a cell and contacting the cell with a compound,wherein the substrate is labeled at the 5′ end with a fluorescent donormoiety and labeled at the 3′ end with a fluorescent acceptor moiety, oralternatively, the substrate is labeled at the 5′ end with a fluorescentacceptor moiety and labeled at the 3′ end with a fluoroscent donormoiety, and measuring the fluorescence of the substrate by, e.g.,fluoresence microscopy or a fluorescence emission detector such as aViewlux or Analyst. The endogenous tRNA splicing endonuclease willcleave the substrate and result in a decrease in the fluorescenceemission by the fluorescent donor moiety and fluorescent acceptor moietyat the wavelength of the fluorescent donor moiety. A compound thatinhibits or reduces the activity of the endogenous tRNA splicingendonuclease will inhibit or reduce cleavage of the substrate and thus,increase the fluorescence emission of the fluorescent acceptor moiety atthe wavelength of the fluorescent donor moiety. A compound that enhancesthe activity of the endogenous tRNA splicing endonuclease will enhancethe cleavage of the substrate and thus, reduce the fluorescence emissionof the fluorescent acceptor moiety at the wavelength of the fluorescentdonor moiety.

Optionally, an agent known to inhibit or reduce the activity of ananimalia tRNA splicing ligase such as an antibody that specificallybinds to an animalia tRNA splicing ligase is included in the contactingstep of the FRET assays to exclude the possibility that the compound issolely inhibiting or reducing the activity of the ligase. Alternatively,an animalia cell or an animalia cell-free extract that is deficient intRNA splicing ligase is used in the FRET assays. As another alternative,ATP may be excluded from the assay. Without being bound by theory, sincethe ligase reaction requires ATP, any effect of a compound in the FRETassay in the absence of ATP cannot be attributed to an effect on theligase reaction and is therefore an effect on an animalia tRNA splicingendonuclease.

In one embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a)microinjecting or transfecting a substrate of a tRNA splicingendonuclease into an animalia cell, wherein the substrate is labeled atthe 5′ end with a fluorophore and labeled at the 3′ end with a quencher,or, alternatively, the substrate is labeled at the 5′ end with aquencher and labeled with a fluorophore; (b) contacting the cell with amember of a library of compounds; and (c) measuring the activity of thetRNA splicing endonuclease, wherein an antiproliferative compound thatinhibits or reduces tRNA splicing activity is identified if afluorescent signal is not detectable in the presence of the compoundrelative to the absence of the compound or the presence of a negativecontrol. In another embodiment, the invention provides a method ofidentifying an antiproliferative compound that inhibits or reducesanimalia tRNA splicing endonuclease activity, said method comprising:(a) contacting an animalia cell containing a substrate of a tRNAsplicing endonuclease with a member of a library of compounds, whereinthe substrate is labeled at the 5′ end with a fluorophore and labeled atthe 3′ end with a quencher, or, alternatively, the substrate is labeledat the 5′ end with a quencher or labeled at the 3′ end with afluorophore; and (b) measuring the activity of the tRNA splicingendonuclease, wherein an antiproliferative compound that inhibits orreduces tRNA splicing activity is identified if a fluorescent signal isnot detectable in the presence of the compound relative to the absenceof the compound or the presence of a negative control.

In another embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a)microinjecting or transfecting a substrate of a tRNA splicingendonuclease into a animalia cell, wherein said substrate is labeled atthe 5′ end with a fluorescent donor moiety and labeled at the 3′ endwith a fluorescent acceptor moiety, or, alternatively, the substrate islabeled with at the 5′ end with a fluorescent acceptor moiety andlabeled at the 3′ end with a fluorescent donor moiety; (b) contactingthe cell with a member of a library of compounds; and (c) measuring theactivity of the tRNA splicing endonuclease, wherein an antiproliferativecompound that inhibits or reduces tRNA splicing activity is identifiedif the fluorescence emission of the fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety in the presence of thecompound is decreaseed relative to the absence of the compound or thepresence of a negative control. In another embodiment, the inventionprovides a method of identifying an antiproliferative compound thatinhibits or reduces animalia tRNA splicing endonuclease activity, saidmethod comprising: (a) contacting an animalia cell containing substrateof a tRNA splicing endonuclease with a member of a library of compounds,wherein the substrate is labeled at the 5′ end with a fluorescent donormoiety and labeled at the 3′ end with a fluorescent acceptor moiety, or,alternatively, the substrate is labeled at the 5′ end with a fluorescentacceptor moiety and labeled at the 3′ end with a fluorescent donormoiety; and (b) measuring the activity of the tRNA splicingendonuclease, wherein an antiproliferative compound that inhibits orreduces tRNA splicing activity is identified if the fluorescenceemission of the fluorescent acceptor moiety at the wavelength of afluorescent donor moiety in the presence of the compound is decreasedrelative to the absence of the compound or the presence of a negativecontrol.

The FRET cell-free-based assays may be conducted by contacting asubstrate for an animalia tRNA splicing endonuclease with an animaliacell-free extract (preferably, a tRNA splicing endonuclease extract) ora purified animalia tRNA splicing endonuclease and a compound, whereinthe substrate is labeled at the 5′ end with a fluorophore and labeled atthe 3′ end with a quencher, or, alternatively, the substrate is labeledat the 5′ end with a quencher and labeled at the 3′ end with afluorophore, and measuring the fluorescence of the substrate by, e.g., afluorescence emission detector such as a Viewlux or Analyst. The tRNAsplicing endonuclease in the animalia cell-free extract or the purifiedanimalia tRNA splicing endonuclease will cleave the substrate and resultin the production of a detectable fluorescent signal. A compound thatinhibits the activity of the animalia tRNA splicing endonuclease willinhibit or reduce the cleavage of the substrate and thus, inhibit orreduce the production of a detectable fluorescent signal. A compoundthat enhances the activity of the animalia tRNA splicing endonucleasewill enhance the cleavage of the substrate and thus, increase theproduction of a detectable fluorescent signal. Alternatively, the FRETcell-free-based assays may be conducted by contacting a substrate for ananimalia tRNA splicing endonuclease with an animalia cell-free extractor a purified animalia tRNA splicing endonuclease and a compound,wherein the substrate is labeled at the 5′ end with a fluorescent donormoiety and labeled at the 3′ end with a fluorescent acceptor moiety, or,alternatively, the substrate is labeled at the 5′ end with a fluorescentacceptor moiety and labeled at the 3′ end with a fluorescent donormoiety, and measuring the fluorescence of the substrate by, e.g., afluorescence emission detector such as a Viewlux or Analyst. The tRNAsplicing endonuclease in the animalia cell-free extract or the purifiedanimalia tRNA splicing endonuclease will cleave the substrate and resultin the production of a detectable fluorescent signal by the fluorescentdonor moiety and fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety. A compound that inhibits the activity of thetRNA splicing endonuclease will inhibit or reduce cleavage of thesubstrate and thus, increase the fluorescence emission of thefluorescent acceptor moiety at the wavelength of the fluorescent donormoiety. A compound that enhances the activity of the endogenous tRNAsplicing endonuclease will enhance the cleavage of the substrate andthus, reduce the fluorescence emission of the fluorescent acceptormoiety at the wavelength of the fluorescent donor moiety.

In one embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a) contactingan animalia cell-free extract (preferably, a tRNA splicing endonucleaseextract) or a purified animalia tRNA splicing endonuclease with asubstrate of a tRNA splicing endonuclease and a member of a library ofcompounds, wherein the substrate is labeled at the 5′ end with afluorophore and at the 3′ end with a quencher, or, alternatively, thesubstrate is labeled at the 5′ end with a quencher and labeled at the 3′end with a fluorophore; and (b) measuring the activity of the tRNAsplicing endonuclease, wherein an antiproliferative compound thatinhibits or reduces tRNA splicing activity is identified if a greaterfluorescent signal is detectable in the presence of the compoundrelative to the absence of the compound or the presence of a negativecontrol. In another embodiment, the invention provides a method ofidentifying an antiproliferative compound that inhibits or reducesanimalia tRNA splicing endonuclease activity, said method comprising:(a) contacting an animalia cell-free extract (preferably, a tRNAsplicing endonuclease extract) or a purified animalia tRNA splicingendonuclease with a substrate of a tRNA splicing endonuclease and amember of a library of compounds, wherein said substrate is labeled atthe 5′ end with a fluorescent donor moiety and labeled at the 3′ endwith a fluorescent acceptor moiety, or, alternatively, the substrate islabeled at the 5′ end with a fluorescent acceptor moiety and labeled atthe 3′ end with a fluorescent donor moiety; and (b) measuring theactivity of the tRNA splicing endonuclease, wherein an antiproliferativecompound that inhibits or reduces tRNA splicing activity is identifiedif the fluorescence emission of the fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety in the presence of thecompound is increased relative to the absence of the compound or thepresence of a negative control

The substrates for a tRNA splicing endonuclease utilized in the FRETassays described herein comprise an intron. In a preferred embodiment,the substrate for a tRNA splicing endonuclease utilized in the FRETassays described herein comprises a tRNA intron. The intron may have abulge-helix-bulge conformation In a preferred embodiment, the substratecomprises a mature domain that contains an intron.

The effect of a compound on the activity of an animalia tRNA splicingendonuclease may be determined utilizing a fluorescencepolarization-based assay. In such an assay, a fluorescently labeledsubstrate for an animalia tRNA splicing endonuclease is contacted withan animalia cell-free extract or a purified animalia tRNA splicingendonuclease and a compound or member of a library of compounds; and thefluorescent polarized light emitted is measured utilizing techniqueswell-known to one of skill in the art or described herein, wherein analteration in the fluorescently polarized light emitted relative to acontrol or the absence of the compound or the member of a library ofcompounds indicates that the compound or member of a library ofcompounds modulates animalia tRNA splicing endonuclease activity.

Further, the effect of a compound on the activity of an animalia tRNAsplicing endonuclease may be determined utilizing a tRNA endonucleasesuppression assay. In such an assay, a host cell is engineered tocontain a reporter gene and a suppressor tRNA, wherein the reporter geneconstruct comprises a reporter gene with a nonsense codon in its openreading frame such that the open reading frame is interrupted and thesuppressor tRNA's expression is regulated by an inducible regulatoryelement and the suppressor tRNA contains a tRNA intron in the antisensecodon; the expression of the suppressor tRNA is induced; the host cellis contacted with a compound; and the expression of the reporter geneand/or the activity of the protein encoded by the reporter gene ismeasured utilizing techniques well-known to one of skill in the art ordescribed herein. A compound that inhibits or reduces the activity of ananimalia tRNA splicing endonuclease will inhibit or reduce theproduction of functional suppressor tRNA and thus, reduce the expressionof the reporter gene relative to a previously determined referencerange, or the expression of the reporter gene in the absence of thecompound or the presence of an appropriate control (e.g., a negativecontrol). A compound that enhances the activity of an animalia tRNAsplicing endonuclease will enhance the production of functionalsuppressor tRNA and thus, enhance the production of the reporter generelative to a previously determined reference range, or the expressionof the reporter gene in the absence of the compound or the presence ofan appropriate control (e.g., a negative control).

The assays of the present invention can be performed using differentincubation times. In a cell-free system, the cell-free extract or thepurified tRNA splicing endonuclease and substrate for animalia tRNAsplicing endonuclease can be incubated together before the addition of acompound or a member of a library of compounds. In certain embodiments,the cell-free extract or the purified animalia tRNA splicingendonuclease are incubated with a substrate for animalia tRNA splicingendonuclease before the addition of a compound or a member of a libraryof compounds for at least 0.2 hours, 0.25 hours, 0.5 hours, 1 hour, 2hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours,18 hours, or at least 1 day. In other embodiments, cell-free extract orpurified animalia tRNA splicing endonuclease, or a substrate foranimalia tRNA splicing endonuclease is incubated with a compound or amember of a library of compounds before the addition of the substrate,or the cell-free extract or the purified animalia tRNA splicingendonuclease, respectively. In certain embodiments, a compound or amember of a library of compounds is incubated with a substrate foranimalia tRNA splicing endonuclease or cell-free extract or purifiedanimalia tRNA splicing endonuclease before the addition of the remainingcomponent, i.e., cell-free extract or purified animalia tRNA splicingendonuclease, or substrate for animalia tRNA splicing endonuclease,respectively, is at least 0.2 hours, 0.25 hours, 0.5 hours, 1 hour, 2hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours,18 hours, or at least 1 day. Once the reaction vessel comprises thethree components, i.e., a compound or a member of a library ofcompounds, the cell-free extract or the purified animalia tRNA splicingendonuclease, and substrate for animalia tRNA splicing endonuclease, thereaction may be further incubated for at least 0.2 hours, 0.25 hours,0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours,10 hours, 12 hours, 18 hours, or at least 1 day.

The progress of the reaction can be measured continuously. For example,if a substrate for animalia tRNA splicing endonuclease or subunits ofanimalia tRNA splicing endonuclease are labeled with fluorophore(s), theprogress of the reaction can be monitored continuously using afluorescence emission detector such as a Viewlux or Analyst.Alternatively, time-points may be taken at different times of thereaction to monitor the progress of the reaction.

Certain assays of the present invention, such as the tRNA endonucleasesuppression assay and the cell-based assays, are indirect assays forcompounds that affect animalia tRNA splicing endonuclease and may detectcompounds that affect another aspect of the tRNA splicing pathway. Inorder to confirm or ensure that a compound is a modulator of an animaliatRNA splicing endonuclease, any assay that measures the direct effect ofthe compound on animalia tRNA splicing endonuclease activity can beperformed. Such assays include assays using purified animalia tRNAsplicing endonuclease and are described below.

The compounds utilized in the assays described herein may be members ofa library of compounds. In specific embodiment, the compound is selectedfrom a combinatorial library of compounds comprising peptoids; randombiooligomers; diversomers such as hydantoins, benzodiazepines anddipeptides; vinylogous polypeptides; nonpeptidal peptidomimetics;oligocarbamates; peptidyl phosphonates; peptide nucleic acid libraries;antibody libraries; carbohydrate libraries; and small organic moleculelibraries. In a preferred embodiment, the small organic moleculelibraries are libraries of benzodiazepines, isoprenoids,thiazolidinones, metathiazanones, pyrrolidines, morpholino compounds, ordiazepindiones.

In certain embodiments, the compounds are screened in pools. Once apositive pool has been identified, the individual compounds of that poolare tested separately. In certain embodiments, the pool size is at least2, at least 5, at least 10, at least 25, at least 50, at least 75, atleast 100, at least 150, at least 200, at least 250, or at least 500compounds.

Once a compound that modulates the activity of a tRNA splicingendonuclease is identified, the structure of the compound may bedetermined utilizing well-known techniques or by referring to apredetermined code. For example, the structure of the compound may bedetermined by mass spectroscopy, NMR, vibrational spectroscopy, or X-raycrystallography.

In certain embodiments, a compound identified in accordance with themethods of the invention may disrupt the interaction of the subunits ofan animalia tRNA splicing endonuclease. In other embodiments, a compoundidentified in accordance with the methods of the invention may insertitself into teh active site of an animalia tRNA splicing endonuclease.

A compound identified in accordance with the methods of the inventionmay directly bind to the tRNA splicing endonuclease. Alternatively, acompound identified in accordance with the methods of invention may bindto the intron. A compound identified in accordance with the methods ofinvention may also disrupt an interaction between a tRNA intron and atRNA splicing endonuclease. Further, a compound identified in accordancewith the methods of the invention may disrupt the interaction betweenthe tRNA mature domain and the tRNA splicing endonuclease. In apreferred embodiment, a compound identified in accordance with themethods of the invention inhibits animalia tRNA splicing endonucleaseactivity. In another preferred embodiment, a compound identified inaccordance with the methods of the invention inhibits preferentiallyinhibits animalia tRNA splicing endonuclease activity.

In certain embodiments of the invention, the compound identified usingthe assays described herein is a small molecule. In a preferredembodiment, the compound identified using the assays described herein isnot known to affect the activity of an animalia tRNA splicingendonuclease. In another preferred embodiment, the compound identifiedusing the assays described herein has not been used as or suggested tobe an anti-proliferative agent or an antifungal agent.

A compound that modulates the activity of a tRNA splicing endonucleasedescribed herein may be tested in in vitro assays or in vivo assays(e.g., cell-based assays or cell-free assays) well-known to one of skillin the art or described herein for the effect of said compound on mRNAtranslation. The compounds identified by the methods of the presentinvention can be screened for their effect on the production of maturetRNA from any of the 28 intron containing human pre-tRNAs. In vitro andin vivo assays well-known to one of skill in the art or described hereinmay be used to determine the antiproliferative effect of a particularcompound on hyperproliferative cells versus normal cells. Further, aparticular compound identified utilizing the assays described herein maybe tested in an animal model for cancer to determine the efficacy of thecompound in the prevention, treatment or amelioration of cancer or asymptom thereof. In addition, the effect of a compound identifiedutilizing the assays described herein may be tested for its effect onyeast tRNA splicing endonculease.

The invention provides for methods for preventing, treating, managing orameliorating a proliferative disorder or a symptom thereof, said methodcomprising administering to a subject in need thereof a therapeuticallyor prophylactically effective amount of a compound, or apharmaceutically acceptable salt thereof, identified according to themethods described herein. In particular, the invention provides for amethod of preventing, treating, managing or ameliorating cancer or asymptom thereof, said method comprising administering to a subject inneed thereof an effective amount of a compound, or a pharmaceuticallyacceptable salt thereof, identified according to the methods describedherein.

In a specific embodiment, the invention provides a method of identifyinga therapeutic agent for the prevention, treatment, management orameliorating of cancer or a symptom thereof, said method comprising: (a)contacting a member of a library of compounds with a cell containing anucleic acid comprising a reporter gene, wherein the reporter genecomprises a tRNA intron; and (b) detecting the expression of saidreporter gene, wherein if a compound that reduces the expression of saidreporter gene relative to a previously determined reference range or theexpression of said reporter gene in the absence of said compound or thepresence of an appropriate control (e.g., a negative control such asPBS) is detected in (b), then (c) contacting the compound with a cancercell or a neoplastic cell and detecting the proliferation of said cancercell or neoplastic cell, so that if the compound reduces or inhibits theproliferation of the cancer cell or neoplastic cell, the compound isidentified as an antiproliferative compound. In accordance with thisembodiment, the compound may be administered to an animal model forcancer and the efficacy of the compound evaluated by assessing, e.g.,proliferation or spread of cancer cells in the animal model.

Without being bound by theory, compounds that target the tRNA splicingendonuclease should only be toxic to highly proliferative transformed,malignant cells, while allowing for normal cellular growth andmetabolism because not all tRNAs require splicing and tRNA splicingoccurs more frequently in proliferating cells. There are only a handfulof tRNA species that require removal of intronic sequences (Trotta, C.R. and Abelson, J. N. tRNA Splicing: An RNA World Add-On or an AncientReaction? In RNA World II, Tom Cech, Ray Gesteland and John Atkins(eds.), Cold Spring Harbor Laboratory Press (1999)). The current versionof the sequence of the human genome has identified 648 tRNA species. Ofthese, only 28 contain an intron that must be removed by the tRNAsplicing endonuclease. The 28 intron containing tRNAs encode 8 differentisoaccepting groups. Seven of these isoaccepting groups containredundant, non-intron-containing versions or can be decoded due towobble rules of the codon-anticodon interaction (Bjork, G. Biosynthesisand Function of modified Nucleoside in tRNA: Structure, Biosynthesis andFunction, D. Soll and V. RayBhandary (eds.), American Society forMicrobiology, Washington D.C. (1995). Thus, this leaves one tRNA as apotential limiting component upon inhibition of tRNA splicing. Bytargeting the tRNA splicing endonuclease, an enzyme dedicated to removalof tRNA introns, the inhibition of tRNA production is fine-tuned to avery few essential tRNA molecules (potentially only a single tRNA).Thus, by inhibiting this process, a very mild toxicity, if any, tonormal cells will be produced, while the ability of rapidlyproliferating transformed cells to divide will be reduced or ablated asa result of the loss in translational capacity.

The invention further provides methods for verifying or confirming theability of a compound to modulate the activity of a tRNA splicingendonuclease. The ability of a compound to modulate the activity of atRNA splicing endonuclease can be verified or confirmed utilizing any ofthe assays described herein to identify such a compound. In a firstembodiment, the invention provides a method for verifying the ability ofa compound to inhibit animalia tRNA splicing endonuclease activity, saidmethod comprising: (a) expressing a nucleic acid comprising a reportergene in a cell, wherein the reporter gene comprises a tRNA intron; (b)contacting said cell with a compound; and (c) detecting the expressionof said reporter gene, wherein a compound that inhibits tRNA splicingendonuclease activity is verified if the expression of said reportergene in the presence of a compound is reduced as compared to theexpression of said reporter gene in the absence of said compound or thepresence of a control.

In another embodiment, the invention provides a method for verifying theability of a compound to inhibit animalia tRNA splicing endonucleaseactivity, said method comprising: (a) contacting a compound with acell-free extract and a nucleic acid comprising a reporter gene, whereinthe reporter gene comprises an intron; and (b) detecting the expressionof said reporter gene, wherein a compound that inhibits tRNA splicingendonuclease activity is verified if the expression of said reportergene in the presence of a compound is reduced as compared to theexpression of said reporter gene in the absence of said compound or thepresence of a control. In another embodiment, the invention provides amethod for verifying the ability of a compound to inhibit animalia tRNAsplicing endonuclease activity, said method comprising: (a) contacting amember of a library of compounds with a cell containing a nucleic acidcomprising a reporter gene, wherein the reporter gene comprises a tRNAintron; and (b) detecting the expression of said reporter gene, whereina compound that inhibits tRNA splicing endonuclease activity is verifiedif the expression of said reporter gene in the presence of a compound isreduced as compared to the expression of said reporter gene in theabsence of said compound or the presence of a control.

3.1 TERMINOLOGY

As used herein, the term “compound” refers to any agent or complex thatis being tested for its ability to modulate tRNA splicing endonucleaseor has been identified as modulating tRNA splicing endonucleaseactivity.

As used herein, the terms “disorder” and “disease” are to refer to acondition in a subject.

As used herein, the term “effective amount” refers to the amount of acompound which is sufficient to reduce or ameliorate the progression,severity and/or duration of a proliferative disorder or one or moresymptoms thereof, prevent the development, recurrence or onset of aproliferative disorder or one or more symptoms thereof, prevent theadvancement of a proliferative disorder or one or more symptoms thereof,or enhance or improve the therapeutic(s) effect(s) of another therapy.

As used herein, the term “fluorescent acceptor moiety” refers to afluorescent compound that absorbs energy from a fluorescent donor moietyand re-emits the transferred energy as fluorescence. Examples offluorescent acceptor moieties include, but are not limited to, coumarinsand related fluorophores, xanthenes (e.g., fluoresceins, rhodols, andrhodamines), resorufins, cyanines, difluoroboradiazindacenes andphthalocyanines.

As used herein, the term “fluorescent donor moiety” refers to afluorescent compound that can absorb energy and is capable oftransferring the energy to an acceptor, such as another fluorescentcompound. Examples of fluorescent donor moieties include, but are notlimited to, coumarins and related dyes, xanthene dyes (e.g.,fluoresceins, rhodols and rhodamines), resorufins, cyanine dyes,bimanes, acridines, isoindoles, dansyl dyes, aminophthalic hydrazides(e.g., luminol and isoluminol derivatives), aminophthalimides,aminonaphthalimides, aminobenzofurans, aminoquinolines,dicyanohydroquinones, fluorescent europium, terbium complexes andrelated compounds.

As used herein, the term “fluorophore” refers to a chromophore thatfluoresces.

As used herein, the term “host cell” refers includes a particularsubject cell transfected with a nucleic acid molecule and the progeny orpotential progeny of such a cell. Progeny of such a cell may not beidentical to the parent cell transfected with the nucleic acid moleculedue to mutations or environmental influences that may occur insucceeding generations or integration of the nucleic acid molecule intothe host cell genome.

As used herein, the term “in combination” refers to the use of more thanone therapy (e.g., prophylactic and/or therapeutic agents). The use ofthe term “in combination” does not restrict the order in which therapies(e.g., prophylactic and/or therapeutic agents) are administered to asubject with a proliferative disorder. A first therapy (e.g., aprophylactic or therapeutic agent such as a compound identified inaccordance with the methods of the invention) can be administered priorto (e.g., 5 minutes, 15 minutes, 30 minutes, 45 minutes, 1 hour, 2hours, 4 hours, 6 hours, 12 hours, 24 hours, 48 hours, 72 hours, 96hours, 1 week, 2 weeks, 3 weeks, 4 weeks, 5 weeks, 6 weeks, 8 weeks, or12 weeks before), concomitantly with, or subsequent to (e.g., 5 minutes,15 minutes, 30 minutes, 45 minutes, 1 hour, 2 hours, 4 hours, 6 hours,12 hours, 24 hours, 48 hours, 72 hours, 96 hours, 1 week, 2 weeks, 3weeks, 4 weeks, 5 weeks, 6 weeks, 8 weeks, or 12 weeks after) theadministration of a second therapy (e.g., a prophylactic or therapeuticagent such as a chemotherapeutic agent or a TNF-α antagonist) to asubject with a proliferative disorder.

As used herein, the term “library” refers to a plurality of compounds. Alibrary can be a combinatorial library, e.g., a collection of compoundssynthesized using combinatorial chemistry techniques, or a collection ofunique chemicals of low molecular weight (less than 1000 daltons) thateach occupy a unique three-dimensional space.

As used herein, the term “ORF” refers to the open reading frame of amRNA, i.e., the region of the mRNA that is translated into protein.

As used herein, the terms “manage”, “managing” and “management” refer tothe beneficial effects that a subject derives from a therapy (e.g., aprophylactic or therapeutic agent) which does not result in a cure ofthe proliferative disorder. In certain embodiments, a subject isadministered one or more therapies to “manage” a disease or disorder soas to prevent the progression or worsening of the disease or disorder.

As used herein, the terms “non-responsive” and refractory” describepatients treated with a currently available therapy (e.g., prophylacticor therapeutic agent) for a proliferative disorder (e.g., cancer), whichis not clinically adequate to relieve one or more symptoms associatedwith such proliferative disorder. Typically, such patients suffer fromsevere, persistently active disease and require additional therapy toameliorate the symptoms associated with their proliferative disoder.

As used herein, the phrase “pharmaceutically acceptable salt(s),”includes, but is not limited to, salts of acidic or basic groups thatmay be present in compounds identified using the methods of the presentinvention. Compounds that are basic in nature are capable of forming awide variety of salts with various inorganic and organic acids. Theacids that can be used to prepare pharmaceutically acceptable acidaddition salts of such basic compounds are those that form non-toxicacid addition salts, i.e., salts containing pharmacologically acceptableanions, including but not limited to sulfuric, citric, maleic, acetic,oxalic, hydrochloride, hydrobromide, hydroiodide, nitrate, sulfate,bisulfate, phosphate, acid phosphate, isonicotinate, acetate, lactate,salicylate, citrate, acid citrate, tartrate, oleate, tannate,pantothenate, bitartrate, ascorbate, succinate, maleate, gentisinate,fumarate, gluconate, glucaronate, saccharate, formate, benzoate,glutamate, methanesulfonate, ethanesulfonate, benzenesulfonate,p-toluenesulfonate and pamoate (i.e.,1,1′-methylene-bis-(2-hydroxy-3-naphthoate)) salts. Compounds thatinclude an amino moiety may form pharmaceutically acceptable salts withvarious amino acids, in addition to the acids mentioned above. Compoundsthat are acidic in nature are capable of forming base salts with variouspharmacologically acceptable cations. Examples of such salts includealkali metal or alkaline earth metal salts and, particularly, calcium,magnesium, sodium lithium, zinc, potassium, and iron salts.

As used herein, the terms “prevent”, “preventing” and “prevention” referto the prevention of the development, recurrence or onset of aproliferative disorder or one or more symptoms thereof resulting fromthe administration of one or more compounds identified in accordance themethods of the invention or the administration of a combination of sucha compound and a known therapy for a proliferative disorder.

As used herein, the term “previously determined reference range” refersto a reference range for the readout of a particular assay. In aspecific embodiment, the term refers to a reference range for theexpression and/or the activity of a reporter gene by a particular cellor in a particular cell-free extract. Each laboratory will establish itsown reference range for each particular assays, each cell type and eachcell-free extract. In a preferred embodiment, at least one positivecontrol and at least one negative control are included in each batch ofcompounds analyzed.

As used herein, the terms “prophylactic agent” and “prophylactic agents”refer to any agent(s) which can be used in the prevention of aproliferative disorder. In certain embodiments, the term “prophylacticagent” refers to a compound identified in the screening assays describedherein. In certain other embodiments, the term “prophylactic agent”refers to an agent other than a compound identified in the screeningassays described herein which is known to be useful for, or has been oris currently being used to prevent or impede the onset, developmentand/or progression of a proliferative disorder or one or more symptomsthereof.

As used herein, the phrase “prophylactically effective amount” refers tothe amount of a therapy (e.g., a prophylactic agent) which is sufficientto result in the prevention of the development, recurrence or onset ofone or more symptoms associated with a proliferative disorder.

As used herein, the term “purified,” in the context of a compound, e.g.a compound identified in accordance with the method of the invention,refers to a compound that is substantially free of chemical precursorsor other chemicals when chemically synthesized. In a specificembodiment, the compound is 60%, preferably 65%, 70%, 75%, 80%, 85%,90%, or 99% free of other, different compounds. In a preferredembodiment, a compound identified in accordance with the methods of theinvention is purified.

As used herein, the term “purified,” in the context of a proteinaceousagent (e.g., a peptide, polypeptide, or protein, such as a tRNA splicingendonuclease or subunit thereof) refers to a proteinaceous agent whichis substantially free of cellular material or contaminating proteinsfrom the cell or tissue source from which it is derived, orsubstantially free of chemical precursors or other chemicals whenchemically synthesized. The language “substantially free of cellularmaterial” includes preparations of a proteinaceous agent in which theproteinaceous agent is separated from cellular components of the cellsfrom which it is isolated or recombinantly produced. Thus, aproteinaceous agent that is substantially free of cellular materialincludes preparations of a proteinaceous agent having less than about30%, 20%, 10%, or 5% (by dry weight) of heterologous protein,polypeptide, peptide, or antibody (also referred to as a “contaminatingprotein”). When the proteinaceous agent is recombinantly produced, it isalso preferably substantially free of culture medium, i.e., culturemedium represents less than about 20%, 10%, or 5% of the volume of theprotein preparation. When the proteinaceous agent is produced bychemical synthesis, it is preferably substantially free of chemicalprecursors or other chemicals, i.e., it is separated from chemicalprecursors or other chemicals which are involved in the synthesis of theproteinaceous agent. Accordingly, such preparations of a proteinaceousagent have less than about 30%, 20%, 10%, 5% (by dry weight) of chemicalprecursors or compounds other than the proteinaceous agent of interest.Preferably, proteinaceous agents disclosed herein are isolated.

As used herein, the term “quencher” refers to a molecule or a part of acompound that is capable of reducing the emission from a fluorescentmoiety. Such reduction includes reducing the light after the time when aphoton is normally emitted from a fluorescent moiety.

As used herein, the term “small molecules” and analogous terms include,but are not limited to, peptides, peptidomimetics, amino acids, aminoacid analogs, polynucleotides, polynucleotide analogs, nucleotides,nucleotide analogs, organic or inorganic compounds (i.e., includingheteroorganic and organometallic compounds) having a molecular weightless than about 10,000 grams per mole, organic or inorganic compoundshaving a molecular weight less than about 5,000 grams per mole, organicor inorganic compounds having a molecular weight less than about 1,000grams per mole, organic or inorganic compounds having a molecular weightless than about 500 grams per mole, organic or inorganic compoundshaving a molecular weight less than about 100 grams per mole, and salts,esters, and other pharmaceutically acceptable forms of such compounds.Salts, esters, and other pharmaceutically acceptable forms of suchcompounds are also encompassed.

As used herein, the terms “subject” and “patient” are usedinterchangeably herein. The terms “subject” and “subjects” refer to ananimal, preferably a mammal including a non-primate (e.g., a cow, pig,horse, cat, dog, rat, and mouse) and a primate (e.g. a chimpanzee, amonkey such as a cynomolgous monkey and a human), and more preferably ahuman. In one embodiment, the subject is refractory or non-responsive tocurrent therapies for a proliferative disorder. In another embodiment,the subject is a farm animal (e.g., a horse, a cow, a pig, etc.) or apet (e.g., a dog or a cat). In a preferred embodiment, the subject is ahuman.

As used herein, the phrase “a substrate for an animalia tRNA splicingendonuclease” refers to any nucleotide sequence recognized and excisedby an animalia tRNA splicing endonuclease. For example, a nucleotidesequence comprising a bulge-helix-bulge structure or a mature domain ofa precursor tRNA may be utilized as a substrate for an animalia tRNAsplicing endonuclease in an assay described herein. A nucleotidesequence recognized and excised by an animalia tRNA splicingendonuclease may comprise 10 nucleotides, 15 nucleotides, 20nucleotides, 25 nucleotides, 25 nucleotides, 30 nucleotides, 40nucleotides, 45 nucleotides, 50 nucleotides, 55 nucleotides, 60nucleotides, 65 nucleotides, 75 nucleotides, 100 nucleotides, 125nucleotides, 150 nucleotides, or more. In a specific embodiment, thesubstrates for a tRNA splicing endonuclease utilized in the assaysdescribed herein comprise a tRNA intron. The substrate may comprise amature domain or a bulge-helix-bulge conformation. In a preferredembodiment, the substrate comprises a mature domain of a precursor tRNA.

A substrate for an animalia tRNA endonuclease may be produced by anymethod well-known to one of skill in the art. For example, the substratemay be chemically synthesized using phosphoramidite or other solution orsolid-phase methods. Detailed descriptions of the chemistry used to formpolynucleotides by the phosphoramidite method are well known (see, e.g.,Caruthers et al., U.S. Pat. Nos. 4,458,066 and 4,415,732; Caruthers etal., 1982, Genetic Engineering 4:1-17; Users Manual Model 392 and 394Polynucleotide Synthesizers, 1990, pages 6-1 through 6-22, AppliedBiosystems, Part No. 901237; Ojwang, et al., 1997, Biochemistry,36:6033-6045). After synthesis, the substrate can be purified usingstandard techniques known to those skilled in the art (see Hwang et al.,1999, Proc. Natl. Acad. Sci. USA 96(23):12997-13002 and references citedtherein). Depending on the length of the substrate and the method of itssynthesis, such purification techniques include, but are not limited to,reverse-phase high-performance liquid chromatography (“reverse-phaseHPLC”), fast performance liquid chromatography (“FPLC”), and gelpurification.

In a specific embodiment, the substrates depicted in FIG. 1 are utilizedin the assays described herein. To generate the hybridized tRNAsubstrate depicted in FIG. 1, both strands of the hybridized substrateare transcribed separately and the two strands are subsequentlyhybridized by heating and cooling. For synthesis of the circularlypermuted tRNA substrate, the RNA is transcribed from the 5′ end in theintron (see FIG. 1C) to the 3′ end in the intron.

As used herein, the term “synergistic” refers to a combination of acompound identified using one of the methods described herein, andanother therapy (e.g., agent) which has been or is currently being usedto prevent, treat, manage or ameliorate a proliferative disorder or asymptom thereof, which is more effective than the additive effects ofthe therapies. A synergistic effect of a combination of therapies (e.g.,prophylactic or therapeutic agents) permits the use of lower dosages ofone or more of the therapies and/or less frequent administration of saidtherapies to a subject with a proliferative disorder. The ability toutilize lower dosages of a therapy (e.g., a prophylactic or therapeuticagent) and/or to administer said therapy less frequently reduces thetoxicity associated with the administration of said agent to a subjectwithout reducing the efficacy of said therapies in the prevention,treatment, management or amelioration of a proliferative disorder. Inaddition, a synergistic effect can result in improved efficacy oftherapies (e.g., agents) in the prevention, treatment, management oramelioration of a proliferative disorder. Finally, a synergistic effectof a combination of therapies (e.g., prophylactic or therapeutic agents)may avoid or reduce adverse or unwanted side effects associated with theuse of either therapy alone.

As used herein, the terms “therapeutic agent” and “therapeutic agents”refer to any agent(s) which can be used in the prevention, treatment,management or amelioration of one or more symptoms of a proliferativedisorder. In certain embodiments, the term “therapeutic agent” refers toa compound identified in the screening assays described herein. In otherembodiments, the term “therapeutic agent” refers to an agent other thana compound identified in the screening assays described herein which isknown to be useful for, or has been or is currently being used toprevent, treat, manage or ameliorate a proliferative disorder or one ormore symptoms thereof.

As used herein, the term “therapeutically effective amount” refers tothat amount of a therapy (e.g., a therapeutic agent) sufficient toresult in the amelioration of one or more symptoms of a proliferativedisorder, prevent advancement of a proliferative disorder, causeregression of the proliferative disorder, or to enhance or improve thetherapeutic effect(s) of another therapy (e.g., therapeutic agent). In aspecific embodiment, with respect to the treatment of cancer, atherapeutically effective amount refers to the amount of a therapy(e.g., a therapeutic agent) that inhibits or reduces the proliferationof cancerous cells, inhibits or reduces the spread of tumor cells(metastasis), inhibits or reduces the onset, development or progressionof one or more symptoms associated with cancer, or reduces the size of atumor. Preferably, a therapeutically effective of a therapy (e.g., atherapeutic agent) reduces the proliferation of cancerous cells or thesize of a tumor by at least 5%, preferably at least 10%, at least 15%,at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, atleast 45%, at least 50%, at least 55%, at least 60%, at least 65%, atleast 70%, at least 75%, at least 80%, at least 85%, at least 90%, atleast 95%, or at least 100% relative to a control such as phosphatebuffered saline (“PBS”).

As used herein, the terms “treat”, “treatment” and “treating” refer tothe reduction or amelioration of the progression, severity and/orduration of a proliferative disorder or one or more symptoms thereofresulting from the administration of one or more compounds identified inaccordance the methods of the invention, or a combination of one or morecompounds identified in accordance with the invention and anothertherapy. In specific embodiments, such terms refer to the inhibition orreduction in the proliferation of cancerous cells, the inhibition orreduction the spread of tumor cells (metastasis), the inhibition orreduction in the onset, development or progression of one or moresymptoms associated with cancer, or the reduction in the size of atumor.

As used herein, the term “tRNA intron” refers to any nucleotide sequencerecognized and excised by an animalia tRNA splicing endonuclease. Inparticular, the term “tRNA intron” refers to an intron typically foundin a precursor tRNA.

As used herein, the term “tRNA splicing endonuclease” refers to theenzyme that is responsible for the recognition of the splice sitescontained in precursor tRNA and the cleavage of the introns present inprecursor tRNA. The archaeal tRNA splicing endonuclease recognizes thebulge-helix-bulge motif in archaeal precursor tRNA. The eukaryotic tRNAsplicing endonuclease recognizes the splice sites contained in precursortRNA by measuring the distance from the mature domain to the splicesites. The eukaryotic tRNA splicing endonuclease also has the capacityto recognize a bulge-helix-bulge motif contained in precursor tRNA. Theyeast tRNA endonuclease is a heterotetramer comprising subunits havingthe molecular masses of 54 kDa (SEN54), 44 kDa (SEN2), 34 kDa (SEN 34),and 15 kDa (SEN 15). The human homologs of the SEN2 and SEN34 subunitshave been identified and the amino acid sequences can be found inGenBank under accession numbers NP_(—)079541 and XP_(—)085899,respectively. In a specific embodiment, the tRNA splicing endonucleaseutilized in the assays described herein is derived from or encodes ananimal tRNA splicing endonuclease (preferably, a mammalian tRNA splicingendonuclease). In a preferred embodiment, the tRNA splicing endonucleaseutilized in the assays described herein is a human tRNA splicingendonuclease.

As used herein, the terms “therapy” and “therapies” refer to any method,protocol and/or agent that can be used in the prevention, treatment,management or amelioration of a disesase or disorder (e.g., aproliferative disorder or a fungal infection) or one or more symptomsthereof. In certain embodiments, such terms refer to chemotherapy,radiation therapy, surgery, supportive therapy and/or other therapiesuseful in the prevention, treatment, management or amelioration of adisease or disorder (e.g., a proliferative disorder or a fungalinfection) or one or more symptoms thereof known to skilled medicalpersonnel.

As used herein, the term “tRNA splicing endonuclease extract” refers toan extract from a cell containing tRNA splicing endonuclease activity.In certain embodiments, a tRNA splicing endonuclease extract is acell-extract containing tRNA splicing endonuclease activity and thecomponents necessary for the transcription and translation of a gene.

Abbreviation

HTS High Throughput Screen

FP fluorescence polarization

FRET Fluorescence Resonance Energy Transfer

HPLC high-performance liquid chromatography

FPLC fast performance liquid chromatography

FACS Fluorescence activated cell sorter

3.2 BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Substrates for HTS Fluorescent screening. The endogenous tRNA isshown in panel A; the hybridized tRNA substrate is shown in panel B; andthe circularly permuted tRNA substrate is shown in panel C. The 5′ ssdesignates the 5′ splice site and 3′ ss designates the 3′ splice site.

FIG. 2: Amino Acid Sequence Alignment of human (Hs Sen 2 (SEQ ID NO: 1)and Hs Sen 2 var. (SEQ ID NO: 2)) and yeast (Sc Sen 2p (SEQ ID NO: 3))tRNA splicing endonuclease Sen 2 submit. The boxed amino acid residuesindicate the YRGGY (SEQ ID NO: 4) active site motif, the circled aminoacid residue indicates the active site histidine, and the underlinedamino acid residues indicate the yeast putative transmembrane domain.

4. DETAILED DESCRIPTION OF THE INVENTION

The present invention provides methods for identifying compounds thatmodulate the activity of an animalia tRNA splicing endonuclease. Inparticular, the invention provides simple, rapid and sensitive methodsfor identifying compounds that inhibit the activity of a mammalian tRNAsplicing endonuclease. The cell-based and cell-free assays describedherein can be utilized in a high throughput format to screen librariesof compounds to identify those compounds that inhibit or reduce theactivity of an animalia tRNA splicing endonuclease.

Reporter gene-based assays can be utilized to identify a compound thatmodulates the activity of an animalia tRNA splicing endonuclease. Thereporter gene-based assays described herein may be conducted bycontacting a compound with a cell genetically engineered to express anucleic acid comprising a reporter gene, wherein said reporter genecomprises a tRNA intron, and measuring the expression of said reportergene. Alternatively, the reporter gene-based assays may be conducted bycontacting a compound with a cell-free extract and a nucleic acidcomprising a reporter gene, wherein said reporter gene comprises a tRNAintron, and measuring the expression of said reporter gene. Thealteration in reporter gene expression relative to a previouslydetermined reference range, or the expression of the reporter gene inthe absence of the compound or an appropriate control (e.g., a negativecontrol) in such reporter-gene based assays indicates that a particularcompound modulates an animalia tRNA splicing endonuclease activity.

FRET assays can be utilized to identify a compound that modulates theactivity of an animalia tRNA splicing endonuclease. The FRET cell-basedassays described herein may be conducted by microinjecting ortransfecting (e.g., using liposomes or electroporation) a substrate foran animalia tRNA splicing endonuclease into a cell and contacting thecell with a compound, wherein the substrate is labeled at the 5′ endwith a fluorophore and labeled at the 3′ end with a quencher, or,alternatively, the substrate is labeled at the 5′ end with a quencherand labeled at the 3′ end with a flurophore, and measuring thefluorescence of the substrate by, e.g., fluorescence microscopy or afluorescence emission detector such as a Viewlux or Analyst. Theendogenous tRNA splicing endonuclease will cleave the substrate andresult in the production of a detectable fluorescent signal. A compoundthat inhibits or reduces the activity of the endogenous tRNA splicingendonuclease will prevent the production of a detectable fluorescentsignal. Alternatively, the FRET cell-based assays may be conducted bymicroinjecting or transfecting a substrate for an animalia tRNA splicingendonuclease into a cell and contacting the cell with a compound,wherein the substrate is labeled at the 5′ end with a fluorescent donormoiety and labeled at the 3′ end with a fluorescent acceptor moiety, or,alternatively, the substrate is labeled at the 5′ end with a fluorescentacceptor moiety and labeled at the 3′ end with a fluorescent donormoiety, and measuring the fluorescence of the substrate by, e.g.,fluorescence microscopy or a fluorescence emission detector such as aViewlux or Analyst. The endogenous tRNA splicing endonuclease willcleave the substrate and result in the production of a detectablefluorescent signal by the fluorescent donor moiety and fluorescentacceptor moiety at the wavelength of the fluorescent donor moiety.However, a compound that inhibits the activity of the endogenous tRNAsplicing endonuclease will reduce the fluorescence emission of thefluorescent acceptor moiety at the wavelength of the fluorescent donormoiety.

The FRET cell-free-based assays may be conducted by contacting asubstrate for an animalia tRNA splicing endonuclease with a cell-freeextract or a purified animalia tRNA splicing endonuclease and acompound, wherein the substrate is labeled at the 5′ end with afluorophore and labeled at the 3′ end with a quencher, or,alternatively, the substrate is labeled at the 5′ end with a quencherand labeled at the 3′ end with a fluorophore, and measuring thefluorescence of the substrate by, e.g., a fluorescence emission detectorsuch as a Viewlux or Analyst. The tRNA splicing will cleave thesubstrate and result in the production of a detectable fluorescentsignal relative to a control. A compound that enhances the activity ofthe tRNA splicing endonuclease will result in the increased fluorescenceemission of a fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety. A compound that inhibits or reduces theactivity of the tRNA splicing endonuclease, however, will prevent orreduce the production of a detectable fluorescent signal relative to acontrol. Alternatively, the FRET cell-free-based assays may be conductedby contacting a substrate for an animalia tRNA splicing endonucleasewith a cell-free extract or a purified animalia tRNA splicingendonuclease and a compound, wherein the substrate is labeled at the 5′end with a fluorescent donor moiety and labeled at the 3′ end with afluorescent acceptor moiety, or, alternatively, the substrate is labeledat the 5′ end with a fluorescent acceptor moiety and labeled at the 3′end with a fluorescent donor moiety, and measuring the fluorescence ofthe substrate by, e.g., a fluorescence emission detector such as aViewlux or Analyst. The tRNA splicing endonuclease will cleave thesubstrate and result in the production of a detectable fluorescentsignal by the fluorescent donor moiety and fluorescent acceptor moietyat the wavelength of the fluorescent donor moiety. A compound thatinhibits or reduces the activity of the tRNA splicing endonuclease willincrease the fluorescence emission of the fluorescent acceptor moiety atthe wavelength of the fluorescent donor moiety. In constrast, a compoundthat enhances the activity of the tRNA splicing endonuclease will reducethe fluorescence emission of the fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety.

A compound may be tested for its ability to enhance or inhibit theactivity of an animalia tRNA endonuclease using a cell-free fluorescencepolarization assay. A substrate of the animalia tRNA endonuclease islabeled on its 5′ or 3′ end such that cleavage by the animalia tRNAendonuclease results in a decrease of size of the labeled portion of thesubstrate and thus in a change of fluoresence polarization. The labeledsubstrate of the animalia tRNA endonuclease is incubated with acell-free extract or a purified animalia tRNA splicing endonuclease anda compound to be tested. A compound that enhances the activity of thetRNA splicing endonuclease activity will increase the rotation of thesubstrate relative to a negative control or the absence of the compound,which will result in more of the light emitted being depolarized. Incontrast, a compound that reduces the activity of the tRNA splicingendonuclease activity will decrease the rotation of the substraterelative to a negative control or the absence of the compound which willresult in the emitted light remaining polarized.

Further a compound may be tested for its ability to enhance or inhibitthe activity of an animalia tRNA endonuclease using a tRNA endonucleasesuppression assay or FISH assay.

The compounds identified in assays described herein that modulateanimalia tRNA splicing endonuclease activity may be tested in in vitroassays (e.g., cell-based assays or cell-free assays) or in vivo assayswell-known to one of skill in the art or described herein for the effectof said compounds on tRNA processing and ultimately mRNA translation. Inparticular, in vitro and in vivo assays well-known to one of skill inthe art or described herein may be used to determine theantiproliferative effect of a particular compound on hyperproliferativecells versus normal cells. Further, a particular compound identifiedutilizing the assays described herein may be tested in an animal modelfor cancer to determine the efficacy of the compound in the prevention,treatment or amelioration of cancer or a symptom thereof. In addition,the effect of a compound identified utilizing the assays describedherein may be tested for its effect on fungal tRNA splicingendonculease.

The structure of the compounds identified in the assays described hereinthat modulate animalia tRNA splicing endonuclease activity can bedetermined utilizing assays well-known to one of skill in the art ordescribed herein. The methods used will depend, in part, on the natureof the library screened. For example, assays or microarrays ofcompounds, each having an address or identifier, may be deconvoluted,e.g., by cross-referencing the positive sample to an original compoundlist that was applied to the individual test assays. Alternatively, thestructure of the compounds identified herein may be determined usingmass spectrometry, nuclear magnetic resonance (“NMR”), X raycrystallography, or vibrational spectroscopy.

The invention encompasses the use of the compounds that inhibit orreduce the activity of an animalia tRNA splicing endonculease which wereidentified in accordance with the methods described herein for theprevention, treatment, management or amelioration of a proliferativedisorder or one or more symptoms thereof. In particular, the inventionencompasses the use of the compounds that inhibit or reduce the activityof an animalia tRNA splicing endonculease which were identified inaccordance with the methods described herein for the prevention,treatment, management or amelioration of cancer or one or more symptomsthereof

4.1 Reporter Gene Constructs, Transfected Cells and Cell Extracts

The invention provides for specific vectors comprising a reporter genecomprising a tRNA intron operably linked to one or more regulatoryelements and host cells transfected with the vectors. The invention alsoprovides for the in vitro translation of a reporter gene flanked by oneor more regulatory elements. Techniques for practicing this specificaspect of this invention will employ, unless otherwise indicated,conventional techniques of molecular biology, microbiology, andrecombinant DNA manipulation and production, which are routinelypracticed by one of skill in the art. See, e.g., Sambrook, 1989,Molecular Cloning, A Laboratory Manual, Second Edition; DNA Cloning,Volumes I and II (Glover, Ed. 1985); Oligonucleotide Synthesis (Gait,Ed. 1984); Nucleic Acid Hybridization (Hames & Higgins, Eds. 1984);Transcription and Translation (Hames & Higgins, Eds. 1984); Animal CellCulture (Freshney, Ed. 1986); Immobilized Cells and Enzymes (IRL Press,1986); Perbal, A Practical Guide to Molecular Cloning (1984); GeneTransfer Vectors for Mammalian Cells (Miller & Calos, Eds. 1987, ColdSpring Harbor Laboratory); Methods in Enzymology, Volumes 154 and 155(Wu & Grossman, and Wu, Eds., respectively), (Mayer & Walker, Eds.,1987); Immunochemical Methods in Cell and Molecular Biology (AcademicPress, London, Scopes, 1987), Expression of Proteins in Mammalian CellsUsing Vaccinia Viral Vectors in Current Protocols in Molecular Biology,Volume 2 (Ausubel et al., Eds., 1991).

4.1.1 Reporter Genes

Any reporter gene well-known to one of skill in the art may be used inreporter gene constructs to ascertain the effect of a compound on ananimalia tRNA endonuclease. Reporter genes refer to a nucleotidesequence encoding a protein that is readily detectable either by itspresence or activity. Reporter genes may be obtained and the nucleotidesequence of the elements determined by any method well-known to one ofskill in the art. The nucleotide sequence of a reporter gene can beobtained, e.g., from the literature or a database such as GenBank.Alternatively, a polynucleotide encoding a reporter gene may begenerated from nucleic acid from a suitable source. If a clonecontaining a nucleic acid encoding a particular reporter gene is notavailable, but the sequence of the reporter gene is known, a nucleicacid encoding the reporter gene may be chemically synthesized orobtained from a suitable source (e.g., a cDNA library, or a cDNA librarygenerated from, or nucleic acid, preferably poly A+ RNA, isolated from,any tissue or cells expressing the reporter gene) by PCR amplification.Once the nucleotide sequence of a reporter gene is determined, thenucleotide sequence of the reporter gene may be manipulated usingmethods well-known in the art for the manipulation of nucleotidesequences, e.g., recombinant DNA techniques, site directed mutagenesis,PCR, etc. (see, for example, the techniques described in Sambrook etal., 1990, Molecular Cloning, A Laboratory Manual, 2d Ed., Cold SpringHarbor Laboratory, Cold Spring Harbor, N.Y. and Ausubel et al., eds.,1998, Current Protocols in Molecular Biology, John Wiley & Sons, NY,which are both incorporated by reference herein in their entireties), togenerate reporter genes having a different amino acid sequence, forexample to create amino acid substitutions, deletions, and/orinsertions.

Examples of reporter genes include, but are not limited to, luciferase(e.g., firefly luciferase, renilla luciferase; and click beetleluciferase), green fluorescent protein (“GFP”) (e.g., green fluorescentprotein, yellow fluorescent protein, red fluorescent protein, cyanfluorescent protein, and blue fluorescent protein), beta-galactosidase(“beta-gal”), beta-glucoronidase, beta-lactamase, chloramphenicolacetyltransferase (“CAT”), and alkaline phosphatase (“AP”). Table 1below lists various reporter genes and the properties of the products ofthe reporter genes that can be assayed. In a preferred embodiment, areporter gene utilized in the reporter constructs is easily assayed andhas an activity which is not normally found in the cell or organism ofinterest. TABLE 1 Reporter Genes and the Properties of the Reporter GeneProducts Reporter Gene Protein Activity & Measurement CAT(chloramphenicol Transfers radioactive acetyl groups toacetyltransferase) chloramphenicol or detection by thin layerchromatography and autoradiography GAL (beta-galactosidase) Hydrolyzescolorless galactosides to yield colored products. GUS (beta- Hydrolyzescolorless glucuronides to yield glucuronidase) colored products. LUC(luciferase) Oxidizes luciferin, emitting photons GFP (green fluorescentFluorescent protein without substrate protein) SEAP (secreted alkalineLuminescence reaction with suitable substrates phosphatase) or withsubstrates that generate chromophores HRP (horseradish In the presenceof hydrogen oxide, oxidation of peroxidase)3,3′,5,5′-tetramethylbenzidine to form a colored complex AP (alkalineLuminescence reaction with suitable substrates phosphatase) or withsubstrates that generate chromophores

Described hereinbelow in further detailed are specific reporter genesand characteristics of those reporter genes.

4.1.1.1 Luciferase

Luciferases are enzymes that emit light in the presence of oxygen and asubstrate (luciferin) and which have been used for real-time, low-lightimaging of gene expression in cell cultures, individual cells, wholeorganisms, and transgenic organisms (reviewed by Greer & Szalay, 2002,Luminescence 17(1):43-74).

As used herein, the term “luciferase” is intended to embrace allluciferases, or recombinant enzymes derived from luciferases which haveluciferase activity. The luciferase genes from fireflies have been wellcharacterized, for example, from the Photinus and Luciola species (see,e.g., International Patent Publication No. WO 95/25798 for Photinuspyralis, European Patent Application No. EP 0 524 448 for Luciolacruciata and Luciola lateralis, and Devine et al., 1993, Biochim.Biophys. Acta 1173(2):121-132 for Luciola mingrelica). Other eucaryoticluciferase genes include, but are not limited to, the click beetle(Photinus plagiophthalamus, see, e.g., Wood et al., 1989, Science244:700-702), the sea panzy (Renilla reniformis, see, e.g., Lorenz etal., 1991, Proc Natl Acad Sci USA 88(10):4438-4442), and the glow worm(Lampyris noctiluca, see e.g., Sula-Newby et al., 1996, Biochem J.313:761-767). The click beetle is unusual in that different members ofthe species emit bioluminescence of different colors, which emit lightat 546 nm (green), 560 nm (yellow-green), 578 nm (yellow) and 593 nm(orange) (see, e.g, U.S. Pat. Nos. 6,475,719; 6,342,379; and 6,217,847,the disclosures of which are incorporated by reference in theirentireties). Bacterial luciferin-luciferase systems include, but are notlimited to, the bacterial lux genes of terrestrial Photorhabdusluminescens (see, e.g., Manukhov et al., 2000, Genetika 36(3):322-30)and marine bacteria Vibrio fischeri and Vibrio harveyi (see, e.g.,Miyamoto et al., 1988, J Biol Chem. 263(26):13393-9, and Cohn et al.,1983, Proc Natl Acad Sci USA., 80(1): 120-3, respectively). Theluciferases encompassed by the present invention also includes themutant luciferases described in U.S. Pat. No. 6,265,177 to Squirrell etal., which is hereby incorporated by reference in its entirety.

In a preferred embodiment, the luciferase is a firefly luciferase, arenilla luciferase, or a click beetle luciferase, as described in anyone of the references listed supra, the disclosures of which areincorporated by reference in their entireties.

4.1.1.2 Green Fluorescent Protein

Green fluorescent protein (“GFP”) is a 238 amino acid protein with aminoacid residues 65 to 67 involved in the formation of the chromophorewhich does not require additional substrates or cofactors to fluoresce(see, e.g., Prasher et al., 1992, Gene 111:229-233; Yang et al., 1996,Nature Biotechnol. 14:1252-1256; and Cody et al., 1993, Biochemistry32:1212-1218).

As used herein, the term “green fluorescent protein” or “GFP” isintended to embrace all GFPs (including the various forms of GFPs whichexhibit colors other than green), or recombinant enzymes derived fromGFPs which have GFP activity. In a preferred embodiment, GFP includesgreen fluorescent protein, yellow fluorescent protein, red fluorescentprotein, cyan fluorescent protein, and blue fluorescent protein. Thenative gene for GFP was cloned from the bioluminescent jellyfishAequorea Victoria (see, e.g., Morin et al., 1972, J. Cell Physiol.77:313-318). Wild type GFP has a major excitation peak at 395 nm and aminor excitation peak at 470 nm. The absorption peak at 470 nm allowsthe monitoring of GFP levels using standard fluorescein isothiocyanate(FITC) filter sets. Mutants of the GFP gene have been found useful toenhance expression and to modify excitation and fluorescence. Forexample, mutant GFPs with alanine, glycine, isoleucine, or threoninesubstituted for serine at position 65 result in mutant GFPs with shiftsin excitation maxima and greater fluorescence than wild type proteinwhen excited at 488 nm (see, e.g., Heim et al., 1995, Nature373:663-664; U.S. Pat. No. 5,625,048; Delagrave et al., 1995,Biotechnology 13:151-154; Cormack et al., 1996, Gene 173:33-38; andCramer et al., 1996, Nature Biotechnol. 14:315-319). The ability toexcite GFP at 488 nm permits the use of GFP with standard fluorescenceactivated cell sorting (“FACS”) equipment. In another embodiment, GFPsare isolated from organisms other than the jellyfish, such as, but notlimited to, the sea pansy, Renilla reriformis.

Techniques for labeling cells with GFP in general are described in U.S.Pat. Nos. 5,491,084 and 5,804,387, which are incorporated by referencein their entireties; Chalfie et al., 1994, Science 263:802-805; Heim etal., 1994, Proc. Natl. Acad. Sci. USA 91:12501-12504; Morise et al.,1974, Biochemistry 13:2656-2662; Ward et al., 1980, Photochem.Photobiol. 31:611-615; Rizzuto et al., 1995, Curr. Biology 5:635-642;and Kaether & Gerdes, 1995, FEBS Lett 369:267-271. The expression ofGFPs in E. coli and C. elegans are described in U.S. Pat. No. 6,251,384to Tan et al., which is incorporated by reference in its entirety. Theexpression of GFP in plant cells is discussed in Hu & Cheng, 1995, FEBSLett 369:331-33, and GFP expression in Drosophila is described in Daviset al., 1995, Dev. Biology 170:726-729.

4.1.1.3 Beta-Galactosidase

Beta galactosidase (“beta-gal”) is an enzyme that catalyzes thehydrolysis of beta-galactosides, including lactose, and the galactosideanalogs o-nitrophenyl-beta-D-galactopyranoside (“ONPG”) and chlorophenolred-beta-D-galactopyranoside (“CPRG”) (see, e.g., Nielsen et al., 1983Proc Natl Acad Sci USA 80(17):5198-5202; Eustice et al., 1991,Biotechniques 11:739-742; and Henderson et al., 1986, Clin. Chem.32:1637-1641). The beta-gal gene functions well as a reporter genebecause the protein product is extremely stable, resistant toproteolytic degradation in cellular lysates, and easily assayed. WhenONPG is used as the substrate, beta-gal activity can be quantitated witha spectrophotometer or microplate reader.

As used herein, the term “beta galactosidase” or “beta-gal” is intendedto embrace all beta-gals, including lacZ gene products, or recombinantenzymes derived from beta-gals which have beta-gal activity. Thebeta-gal gene functions well as a reporter gene because the proteinproduct is extremely stable, resistant to proteolytic degradation incellular lysates, and easily assayed. In an embodiment where ONPG is thesubstrate, beta-gal activity can be quantitated with a spectrophotometeror microplate reader to determine the amount of ONPG converted at 420nm. In an embodiment when CPRG is the substrate, beta-gal activity canbe quantitated with a spectrophotometer or microplate reader todetermine the amount of CPRG converted at 570 to 595 nm. In yet anotherembodiment, the beta-gal activity can be visually ascertained by platingbacterial cells transformed with a beta-gal construct onto platescontaining Xgal and IPTG. Bacterial colonies that are dark blue indicatethe presence of high beta-gal activity and colonies that are varyingshades of blue indicate varying levels of beta-gal activity.

4.1.1.4 Beta-Glucoronidase

Beta-glucuronidase (“GUS”) catalyzes the hydrolysis of a very widevariety of beta-glucuronides, and, with much lower efficiency,hydrolyzes some beta-galacturonides. GUS is very stable, will toleratemany detergents and widely varying ionic conditions, has no cofactors,nor any ionic requirements, can be assayed at any physiological pH, withan optimum between 5.0 and 7.8, and is reasonably resistant to thermalinactivation (see, e.g., U.S. Pat. No. 5,268,463, which is incorporatedby reference in its entirety).

In one embodiment, the GUS is derived from the Esherichia colibeta-glucuronidase gene. In alternate embodiments of the invention, thebeta-glucuronidase encoding nucleic acid is homologous to the E. colibeta-glucuronidase gene and/or may be derived from another organism orspecies.

GUS activity can be assayed either by fluorescence or spectrometry, orany other method described in U.S. Pat. No. 5,268,463, the disclosure ofwhich is incorporated by reference in its entirety. For a fluorescentassay, 4-trifluoromethylumbelliferyl beta-D-glucuronide is a verysensitive substrate for GUS. The fluorescence maximum is close to 500nm—bluish green, where very few plant compounds fluoresce or absorb.4-trifluoromethylumbelliferyl beta-D-glucuronide also fluoresces muchmore strongly near neutral pH, allowing continuous assays to beperformed more readily than with MUG. 4-trifluoromethylumbelliferylbeta-D-glucuronide can be used as a fluorescent indicator in vivo. Thespectrophotometric assay is very straightforward and moderatelysensitive (Jefferson et al., 1986, Proc. Natl. Acad. Sci. USA86:8447-8451). A preferred substrate for spectrophotometric measurementis p-nitrophenyl beta-D-glucuronide, which when cleaved by GUS releasesthe chromophore p-nitrophenol. At a pH greater than its pK_(a) (around7.15) the ionized chromophore absorbs light at 400-420 nm, giving ayellow color.

4.1.1.5 Beta-Lactamase

Beta-lactamases are nearly optimal enzymes in respect to their almostdiffusion-controlled catalysis of beta-lactam hydrolysis, making themsuited to the task of an intracellular reporter enzyme (see, e.g.,Christensen et al., 1990, Biochem. J. 266: 853-861). They cleave thebeta-lactam ring of beta-lactam antibiotics, such as penicillins andcephalosporins, generating new charged moieties in the process (see,e.g., O'Callaghan et al., 1968, Antimicrob. Agents. Chemother. 8: 57-63and Stratton, 1988, J. Antimicrob. Chemother. 22, Suppl. A: 23-35). Alarge number of beta-lactamases have been isolated and characterized,all of which would be suitable for use in accordance with the presentinvention (see, e.g, Richmond & Sykes, 1978, Adv. Microb. Physiol.9:31-88 and Ambler, 1980, Phil. Trans. R. Soc. Lond. [Ser. B.] 289:321-331, the disclosures of which are incorporated by reference in theirentireties).

The coding region of an exemplary beta-lactamase employed has beendescribed in U.S. Pat. No. 6,472,205, Kadonaga et al., 1984, J. Biol.Chem. 259: 2149-2154, and Sutcliffe, 1978, Proc. Natl. Acad. Sci. USA75: 3737-3741, the disclosures of which re incorporated by reference intheir entireties. As would be readily apparent to those skilled in thefield, this and other comparable sequences for peptides havingbeta-lactamase activity would be equally suitable for use in accordancewith the present invention. The combination of a fluorogenic substratedescribed in U.S. Pat. Nos. 6,472,205, 5,955,604, and 5,741,657, thedisclosures of which are incorporated by reference in their entireties,and a suitable beta-lactamase can be employed in a wide variety ofdifferent assay systems, such as are described in U.S. Pat. No.4,740,459, which is hereby incorporated by reference in its entirety.

4.1.1.6 Chloramphenicol Acetyltransferase

Chloramphenicol acetyl transferase (“CAT”) is commonly used as areporter gene in mammalian cell systems because mammalian cells do nothave detectable levels of CAT activity. The assay for CAT involvesincubating cellular extracts with radiolabeled chloramphenicol andappropriate co-factors, separating the starting materials from theproduct by, for example, thin layer chromatography (“TLC”), followed byscintillation counting (see, e.g., U.S. Pat. No. 5,726,041, which ishereby incorporated by reference in its entirety).

As used herein, the term “chloramphenicol acetyltransferase” or “CAT” isintended to embrace all CATs, or recombinant enzymes derived from CATwhich have CAT activity. While it is preferable that a reporter systemwhich does not require cell processing, radioisotopes, andchromatographic separations would be more amenable to high through-putscreening, CAT as a reporter gene may be preferable in situations whenstability of the reporter gene is important. For example, the CATreporter protein has an in vivo half life of about 50 hours, which isadvantageous when an accumulative versus a dynamic change type of resultis desired.

4.1.1.7 Secreted Alkaline Phosphatase

The secreted alkaline phosphatase (“SEAP”) enzyme is a truncated form ofalkaline phosphatase, in which the cleavage of the transmembrane domainof the protein allows it to be secreted from the cells into thesurrounding media. In a preferred embodiment, the alkaline phosphataseis isolated from human placenta.

As used herein, the term “secreted alkaline phosphatase” or “SEAP” isintended to embrace all SEAP or recombinant enzymes derived from SEAPwhich have alkaline phosphatase activity. SEAP activity can be detectedby a variety of methods including, but not limited to, measurement ofcatalysis of a fluorescent substrate, immunoprecipitation, BPLC, andradiometric detection. The luminescent method is preferred due to itsincreased sensitivity over calorimetric detection methods. Theadvantages of using SEAP is that a cell lysis step is not required sincethe SEAP protein is secreted out of the cell, which facilitates theautomation of sampling and assay procedures. A cell-based assay usingSEAP for use in cell-based assessment of inhibitors of the Hepatitis Cvirus protease is described in U.S. Pat. No. 6,280,940 to Potts et al.which is hereby incorporated by reference in its entirety.

4.1.2 tRNA Introns

Any nucleotide sequence recognized and excised by an animalia tRNAsplicing endonuclease may be inserted into the coding region of areporter gene such that the mRNA coding the reporter gene out of frameutilizing well-known molecular biology techniques. For example, anucleotide sequence comprising a bulge-helix-bulge structure or a maturedomain of a precursor tRNA may be inserted into the coding region of areporter gene such that the mRNA coding the reporter gene out of frame.Alternatively, a nucleotide sequence recognized and excised by ananimalia tRNA splicing endonuclease may be inserted into the 5′untranslated region, 3′ untranslated region or both the 5′ and 3′untranslated regions of a reporter gene construct. A nucleotide sequencerecognized and excised by an animalia tRNA splicing endonuclease maycomprise 10 nucleotides, 15 nucleotides, 20 nucleotides, 25 nucleotides,25 nucleotides, 30 nucleotides, 40 nucleotides, 45 nucleotides, 50nucleotides, 55 nucleotides, 60 nucleotides, 65 nucleotides, 75nucleotides, 100 nucleotides, 125 nucleotides, 150 nucleotides, or more.In certain embodiments, the nucleotide sequence is at least 10nucleotides in length.

In a specific embodiment, a tRNA intron is inserted within the openreading frame of a reporter gene. In another embodiment, two, three,four, five or more tRNA introns are inserted within the open readingframe of a reporter gene. In an alternative embodiment, a tRNA intron isinserted within the 5′ untranslated region, 3′ untranslated region orboth the 5′ and 3′ untranslated region of a reporter gene construct. Inan alternative embodiment, two, three, four, five or more tRNA intronsare inserted within the 5′ untranslated region, 3′ untranslated regionor both the 5′ and 3′ untranslated region of a reporter gene construct.The tRNA intron may comprise a bulge-helix-bulge conformation.

A reporter gene containing a tRNA intron may be produced by any methodwell-known to one of skill in the art. For example, the reporter genecontaining a tRNA intron may be chemically synthesized usingphosphoramidite or other solution or solid-phase methods. Detaileddescriptions of the chemistry used to form polynucleotides by thephosphoramidite method are well known (see, e.g., Caruthers et al., U.S.Pat. Nos. 4,458,066 and 4,415,732; Caruthers et al., 1982, GeneticEngineering 4:1-17; Users Manual Model 392 and 394 PolynucleotideSynthesizers, 1990, pages 6-1 through 6-22, Applied Biosystems, Part No.901237; Ojwang, et al., 1997, Biochemistry, 36:6033-6045). Aftersynthesis, the reporter gene containing a tRNA intron can be purifiedusing standard techniques known to those skilled in the art (see Hwanget al., 1999, Proc. Natl. Acad. Sci. USA 96(23):12997-13002 andreferences cited therein). Depending on the length of the reporter genecontaining a tRNA intron and the method of its synthesis, suchpurification techniques include, but are not limited to, reverse-phasehigh-performance liquid chromatography (“reverse-phase HPLC”), fastperformance liquid chromatography (“FPLC”), and gel purification.Methods for labeling the substrate with a fluorescent acceptor moiety, afluorescent donor moiety and/or quencher are well-known in the art (see,e.g., U.S. Pat. Nos. 6,472,156, 6,451,543, 6,348,322, 6,342,379,6,323,039, 6,297,018, 6,291,201, 6,280,981, 5,843,658, and 5,439,797,the disclosures of which are incorporated by reference in theirentirety).

4.1.3 Vectors

The nucleotide sequence coding for a reporter gene and the nucleotidesequence coding for a tRNA intron can be inserted into an appropriateexpression vector, i.e., a vector which contains the necessary elementsfor the transcription and translation of the inserted protein-codingsequence. The necessary transcriptional and translational signals canalso be supplied by the reporter gene. A variety of host-vector systemsmay be utilized to express the reporter gene. These include, but are notlimited to, mammalian cell systems infected with virus (e.g., vacciniavirus, adenovirus, etc.); insect cell systems infected with virus (e.g.,baculovirus); microorganisms such as yeast containing yeast vectors, orbacteria transformed with bacteriophage, DNA, plasmid DNA, or cosmidDNA; and stable cell lines generated by transformation using aselectable marker. The expression elements of vectors vary in theirstrengths and specificities. Depending on the host-vector systemutilized, any one of a number of suitable transcription and translationelements may be used.

Any of the methods previously described for the insertion of DNAfragments into a vector may be used to construct expression vectorscontaining a chimeric nucleic acid consisting of appropriatetranscriptional/translational control signals and the protein codingsequences. These methods may include in vitro recombinant DNA andsynthetic techniques and in vivo recombinants (genetic recombination).Expression of the reporter gene construct may be regulated by a secondnucleic acid sequence so that the reporter gene is expressed in a hosttransformed with the recombinant DNA molecule. For example, expressionof a reporter gene construct may be controlled by any promoter/enhancerelement known in the art, such as a constitutive promoter, atissue-specific promoter, or an inducible promoter. Specific examples ofpromoters which may be used to control gene expression include, but arenot limited to, the SV40 early promoter region (Bernoist & Chambon,1981, Nature 290:304-310), the promoter contained in the 3′ longterminal repeat of Rous sarcoma virus (Yamamoto et al., 1980, Cell22:787-797), the herpes thymidine kinase promoter (Wagner et al., 1981,Proc. Natl. Acad. Sci. U.S.A 78:1441-1445), the regulatory sequences ofthe metallothionein gene (Brinster et al., 1982, Nature 296:39-42);prokaryotic expression vectors such as the β-lactamase promoter(Villa-Kamaroff et al., 1978, Proc. Natl. Acad. Sci. U.S.A.75:3727-3731), or the tac promoter (DeBoer et al., 1983, Proc. Natl.Acad. Sci. U.S.A. 80:21-25); see also “Useful proteins from recombinantbacteria” in Scientific American, 1980, 242:74-94; plant expressionvectors comprising the nopaline synthetase promoter region(Herrera-Estrella et al., Nature 303:209-213) or the cauliflower mosaicvirus 35S RNA promoter (Gardner, et al., 1981, Nucl. Acids Res. 9:2871),and the promoter of the photosynthetic enzyme ribulose biphosphatecarboxylase (Herrera-Estrella et al., 1984, Nature 310:115-120);promoter elements from yeast or other fungi such as the Gal 4 promoter,the ADC (alcohol dehydrogenase) promoter, PGK (phosphoglycerol kinase)promoter, alkaline phosphatase promoter, and the following animaltranscriptional control regions, which exhibit tissue specificity andhave been utilized in transgenic animals: elastase I gene control regionwhich is active in pancreatic acinar cells (Swift et al., 1984, Cell38:639-646; Ornitz et al., 1986, Cold Spring Harbor Symp. Quant. Biol.50:399-409; MacDonald, 1987, Hepatology 7:425-515); insulin gene controlregion which is active in pancreatic beta cells (Hanahan, 1985, Nature315:115-122), immunoglobulin gene control region which is active inlymphoid cells (Grosschedl et al., 1984, Cell 38:647-658; Adames et al.,1985, Nature 318:533-538; Alexander et al., 1987, Mol. Cell. Biol.7:1436-1444), mouse mammary tumor virus control region which is activein testicular, breast, lymphoid and mast cells (Leder et al., 1986, Cell45:485-495), albumin gene control region which is active in liver(Pinkert et al., 1987, Genes and Devel. 1:268-276), alpha-fetoproteingene control region which is active in liver (Krumlauf et al., 1985,Mol. Cell. Biol. 5:1639-1648; Hammer et al., 1987, Science 235:53-58;alpha 1-antitrypsin gene control region which is active in the liver(Kelsey et al., 1987, Genes and Devel. 1:161-171), beta-globin genecontrol region which is active in myeloid cells (Mogram et al., 1985,Nature 315:338-340; Kollias et al., 1986, Cell 46:89-94; myelin basicprotein gene control region which is active in oligodendrocyte cells inthe brain (Readhead et al., 1987, Cell 48:703-712); myosin light chain-2gene control region which is active in skeletal muscle (Sani, 1985,Nature 314:283-286), and gonadotropic releasing hormone gene controlregion which is active in the hypothalamus (Mason et al., 1986, Science234:1372-1378).

In a specific embodiment, a vector is used that comprises a promoteroperably linked to a reporter gene, one or more origins of replication,and, optionally, one or more selectable markers (e.g., an antibioticresistance gene). In a preferred embodiment, the vectors are CMVvectors, T7 vectors, lac vectors, pCEP4 vectors, 5.0/F vectors, orvectors with a tetracycline-regulated promoter (e.g., pcDNA™5/FRT/TOfrom Invitrogen

Expression vectors containing the reporter gene construct of the presentinvention can be identified by three general approaches: (a) nucleicacid hybridization, (b) presence or absence of “marker” nucleic acidfunctions, (c) expression of inserted sequences, and (d) sequencing. Inthe first approach, the presence of the reporter gene inserted in anexpression vector can be detected by nucleic acid hybridization usingprobes comprising sequences that are homologous to the inserted reportergene. In the second approach, the recombinant vector/host system can beidentified and selected based upon the presence or absence of certain“marker” nucleic acid functions (e.g., thymidine kinase activity,resistance to antibiotics, transformation phenotype, occlusion bodyformation in baculovirus, etc.) caused by the insertion of the nucleicacid of interest, i.e., the reporter gene construct, in the vector. Forexample, if the nucleic acid of interest is inserted within the markernucleic acid sequence of the vector, recombinants containing the insertcan be identified by the absence of the marker nucleic acid function. Inthe third approach, recombinant expression vectors can be identified byassaying the reporter gene product expressed by the recombinant. Suchassays can be based, for example, on the physical or functionalproperties of the particular reporter gene.

In a preferred embodiment, the reporter gene constructs are cloned intostable cell line expression vectors. In a preferred embodiment, thestable cell line expression vector contains a site specific genomicintegration site. In another preferred embodiment, the reporter geneconstruct is cloned into an episomal mammalian expression vector.

4.1.4 Transfection

Once a vector encoding the appropriate gene has been synthesized, a hostcell is transformed or transfected with the vector of interest. The useof stable transformants is preferred. In a preferred embodiment, thehost cell is a mammalian cell. In a more preferred embodiment, the hostcell is a human cell. In another embodiment, the host cells are primarycells isolated from a tissue or other biological sample of interest.Host cells that can be used in the methods of the present inventioninclude, but are not limited to, hybridomas, pre-B cells, 293 cells,293T cells, HeLa cells, HepG2 cells, K562 cells, 3T3 cells. In anotherpreferred embodiment, the host cells are immortalized cell lines derivedfrom a source, e.g., a tissue. Other host cells that can be used in thepresent invention include, but are not limited to, virally-infectedcells.

Transformation may be by any known method for introducingpolynucleotides into a host cell, including, for example packaging thepolynucleotide in a virus and transducing a host cell with the virus,and by direct uptake of the polynucleotide. The transformation procedureused depends upon the host to be transformed. Mammalian transformations(i.e., transfections) by direct uptake may be conducted using thecalcium phosphate precipitation method of Graham & Van der Eb, 1978,Virol. 52:546, or the various known modifications thereof. Other methodsfor introducing recombinant polynucleotides into cells, particularlyinto mammalian cells, include dextran-mediated transfection, calciumphosphate mediated transfection, polybrene mediated transfection,protoplast fusion, electroporation, encapsulation of thepolynucleotide(s) in liposomes, and direct microinjection of thepolynucleotides into nuclei. Such methods are well-known to one of skillin the art.

In a preferred embodiment, stable cell lines containing the constructsof interest are generated for high throughput screening. Such stablecells lines may be generated by introducing a reporter gene constructcomprising a selectable marker, allowing the cells to grow for 1-2 daysin an enriched medium, and then growing the cells on a selective medium.The selectable marker in the recombinant plasmid confers resistance tothe selection and allows cells to stably integrate the plasmid intotheir chromosomes and grow to form foci which in turn can be cloned andexpanded into cell lines.

A number of selection systems may be used, including but not limited tothe herpes simplex virus thymidine kinase (Wigler, et al., 1977, Cell11:223), hypoxanthine-guanine phosphoribosyltransferase (Szybalska &Szybalski, 1962, Proc. Natl. Acad. Sci. USA 48:2026), and adeninephosphoribosyltransferase (Lowy, et al., 1980, Cell 22:817) genes can beemployed in tk-, hgprt- or aprt-cells, respectively. Also,anti-metabolite resistance can be used as the basis of selection fordhfr, which confers resistance to methotrexate (Wigler, et al., 1980,Natl. Acad. Sci. USA 77:3567; O'Hare, et al., 1981, Proc. Natl. Acad.Sci. USA 78:1527); gpt, which confers resistance to mycophenolic acid(Mulligan & Berg, 1981, Proc. Natl. Acad. Sci. USA 78:2072); neo, whichconfers resistance to the aminoglycoside G-418 (Colberre-Garapin, etal., 1981, J. Mol. Biol. 150:1); and hygro, which confers resistance tohygromycin (Santerre, et al., 1984, Gene 30:147) genes.

4.1.5 Cell-Free Extracts

The invention provides for the translation of the reporter geneconstructs in a cell-free system. Techniques for practicing thisspecific aspect of this invention will employ, unless otherwiseindicated, conventional techniques of molecular biology, microbiology,and recombinant DNA manipulation and production, which are routinelypracticed by one of skill in the art. See, e.g., Sambrook, 1989,Molecular Cloning, A Laboratory Manual, Second Edition; DNA Cloning,Volumes I and II (Glover, Ed. 1985); and Transcription and Translation(Hames & Higgins, Eds. 1984).

Any technique well-known to one of skill in the art may be used togenerate cell-free extracts for translation in vitro. For example, thecell-free extracts for in vitro translation reactions can be generatedby centrifuging cells and clarifying the supernatant. In particular, acell extract utilized in accordance with the invention may be an S1extract (i.e., the supernatant from a 1,000×g spin) to an S500 extract(i.e., the supernatant from a 500,000×g spin), preferably an S10 extract(i.e., the supernatant from a 10,000×g spin) to an S250 extract (i.e.,the supernatant from a 250,000×g spin). In a specific embodiment, a cellextract utilized in accordance with the invention is an S50 extract(i.e., the supernatant from a 50,000×g spin) to an S100 extract (i.e.,the supernatant from a 100,000×g spin).

The cell-free translation extract may be isolated from cells of anyspecies origin. For example, the cell-free translation extract may beisolated from human cells, cultured mouse cells, cultured rat cells,Chinese hamster ovary (CHO) cells, Xenopus oocytes, rabbitreticulocytes, wheat germ, or rye embryo (see, e.g., Krieg & Melton,1984, Nature 308:203 and Dignam et al., 1990 Methods Enzymol.182:194-203). Alternatively, the cell-free translation extract, e.g.,rabbit reticulocyte lysates and wheat germ extract, can be purchasedfrom, e.g., Promega, (Madison, Wis.). In a preferred embodiment, thecell-free extract is an extract isolated from human cells. In a morepreferred embodiment, the human cells are HeLa cells.

4.2 Purification of tRNA Splicing Endonuclease

Animalia tRNA splicing endonuclease or a subunit thereof, preferablymammalian, more preferably human, can be expressed and purified by anymethod known to the skilled artisan. Animalia tRNA splicing endonucleasecan be expressed by recombinant DNA technology. In specific embodiments,the animalia tRNA splicing endonuclease is fused to a peptide tag tofacilitate purification of the animalia tRNA splicing endonuclease. Inother embodiments, the endogenous animalia tRNA splicing endonuclease ispurified.

In certain embodiments, recombinant human tRNA splicing endonuclease ispurified and used with the methods of the invention. In otherembodiments, partially purified human tRNA splicing endonuclease fromany human cell source is used with the methods of the invention.

4.2.1 Recombinant DNA

In various embodiments, an animalia tRNA splicing endonuclease subunitis encoded by a specific nucleotide sequence which is to be transcribedand translated. The nucleotide sequence is inserted into an expressionvector for propagation and expression in recombinant cells. An animaliatRNA splicing endonuclease is a heterotetramer, each of the foursubunits may be expressed together in the same cell or separately indifferent cells; the subunits isolated and then combined to produce tRNAsplicing endonuclease. Preferably, the animalia tRNA splicingendonuclease subunits are expressed in the same cell and the functionaltRNA splicing endonuclease is isolated from the cell.

An expression construct, as used herein, refers to a nucleotide sequenceencoding one, two, three or four animalia tRNA splicing endonucleasesubunits (preferably, human tRNA splicing endonuclease subunits)operably linked to one or more regulatory regions or enhancer/promotersequences which enables the expression of animalia tRNA splicingendonuclease subunits in an appropriate host cell. “Operably linked”refers to an association in which the regulatory regions and thenucleotide sequence encoding an animalia tRNA splicing endonucleasesubunit that is to be expressed are joined and positioned in such a wayas to permit transcription, and ultimately, translation.

The regulatory regions necessary for transcription of an animalia tRNAsplicing endonuclease subunit can be provided by the expression vector.In a compatible host-construct system, cellular transcriptional factors,such as RNA polymerase, will bind to the regulatory regions on theexpression construct to effect transcription of an animalia tRNAsplicing endonuclease subunit in the host organism. The precise natureof the regulatory regions needed for gene expression may vary from hostcell to host cell. Generally, a promoter is required which is capable ofbinding RNA polymerase and promoting the transcription of anoperably-associated nucleic acid sequence. Such regulatory regions mayinclude those 5′-non-coding sequences involved with initiation oftranscription and translation, such as the TATA box, capping sequence,CAAT sequence, and the like. The non-coding region 3′ to the codingsequence may contain transcriptional termination regulatory sequences,such as terminators and polyadenylation sites.

Constitutive, tissue-specific and/or inducible regulatory regions may beused for expression of an animalia tRNA splicing endonuclease subunit.It may be desirable to use inducible promoters when the conditionsoptimal for growth of the host cells and the conditions for high levelexpression of the animalia tRNA splicing endonuclease subunit aredifferent. Examples of useful regulatory regions are provided below.

In order to attach DNA sequences with regulatory functions, such aspromoters, to the sequence encoding an animalia tRNA splicingendonuclease subunit or to insert the sequence encoding an animalia tRNAsplicing endonuclease subunit into the cloning site of a vector, linkersor adapters providing the appropriate compatible restriction sites maybe ligated to the ends of the cDNAs by techniques well known in the art(Wu et al., 1987, Methods in Enzymol 152:343-349). Cleavage with arestriction enzyme can be followed by modification to create blunt endsby digesting back or filling in single-stranded DNA termini beforeligation. Alternatively, a desired restriction enzyme site can beintroduced into a fragment of DNA by amplification of the DNA by use ofPCR with primers containing the desired restriction enzyme site.

An expression construct comprising a sequence encoding an animalia tRNAsplicing endonuclease subunit operably linked to regulatory regions(enhancer/promoter sequences) can be directly introduced intoappropriate host cells for expression and production of an animalia tRNAsplicing endonuclease subunit without further cloning. The expressionconstructs can also contain DNA sequences that facilitate integration ofthe sequence encoding an animalia tRNA splicing endonuclease subunitinto the genome of the host cell, e.g. via homologous recombination. Inthis instance, it is not necessary to employ an expression vectorcomprising a replication origin suitable for appropriate host cells inorder to propagate and express an animalia tRNA splicing endonucleasesubunit in the host cells.

A variety of expression vectors may be used in the present inventionwhich include, but are not limited to, plasmids, cosmids, phage,phagemids, or modified viruses. Typically, such expression vectorscomprise a functional origin of replication for propagation of thevector in an appropriate host cell, one or more restriction endonucleasesites for insertion of the sequence encoding the animalia tRNA splicingendonuclease subunit, and one or more selection markers. The expressionvector must be used with a compatible host cell which may be derivedfrom a prokaryotic or an eukaryotic organism including but not limitedto bacteria, yeasts, insects, mammals, and humans.

Vectors based on E. coli are the most popular and versatile systems forhigh level expression of foreign proteins (Makrides, 1996, MicrobiolRev, 60:512-538). Non-limiting examples of regulatory regions that canbe used for expression in E. coli may include but not limited to lac;trp, lpp, phoA, recA, tac, T3, T7 and λP_(L) (Makrides, 1996, MicrobiolRev, 60:512-538). Non-limiting examples of prokaryotic expressionvectors may include the λgt vector series such as λgt11 (Huynli et al.,1984 in “DNA Cloning Techniques”, Vol. I: A Practical Approach (D.Glover, ed.), pp. 49-78, IRL Press, Oxford), and the pET vector series(Studier et al., 1990, Methods Enzymol., 185:60-89). However, apotential drawback of a prokaryotic host-vector system is the inabilityto perform many of the post-translational processing of mammalian cells.Thus, an eukaryotic host-vector system is preferred, a mammalianhost-vector system is more preferred, and a human host-vector system isthe most preferred.

For expression of an animalia tRNA splicing endonuclease subunit inmammalian host cells, a variety of regulatory regions can be used, forexample, the SV40 early and late promoters, the cytomegalovirus (CMV)immediate early promoter, and the Rous sarcoma virus long terminalrepeat (RSV-LTR) promoter. Inducible promoters that may be useful inmammalian cells include but are not limited to those associated with themetallothionein II gene, mouse mammary tumor virus glucocorticoidresponsive long terminal repeats (MMTV-LTR), β-interferon gene, andhsp70 gene (Williams et al., 1989, Cancer Res. 49:2735-42; Taylor etal., 1990, Mol. Cell Biol., 10:165-75). It may be advantageous to useheat shock promoters or stress promoters to drive expression of ananimalia tRNA splicing endonuclease subunit in recombinant host cells.

In addition, the expression vector may contain selectable or screenablemarker genes for initially isolating, identifying or tracking host cellsthat contain DNA encoding the elected animalia tRNA splicingendonuclease subunit. For long term, high yield production of ananimalia tRNA splicing endonuclease subunit, stable expression inmammalian cells is preferred. A number of selection systems may be usedfor mammalian cells, including but not limited to the Herpes simplexvirus thymidine kinase (Wigler et al., 1977, Cell 11:223),hypoxanthine-guanine phosphoribosyltransferase (Szybalski and Szybalski,1962, Proc. Natl. Acad. Sci. USA 48:2026), and adeninephosphoribosyltransferase (Lowy et al., 1980, Cell 22:817) genes can beemployed in tk⁻, hgprt⁻ or aprt⁻ cells, respectively. Also,antimetabolite resistance can be used as the basis of selection fordihydrofolate reductase (dhfr), which confers resistance to methotrexate(Wigler et al., 1980, Natl. Acad. Sci. USA 77:3567; O'Hare et al., 1981,Proc. Natl. Acad. Sci. USA 78:1527); gpt, which confers resistance tomycophenolic acid (Mulligan & Berg, 1981, Proc. Natl. Acad. Sci. USA78:2072); neomycin phosphotransferase (neo), which confers resistance tothe aminoglycoside G-418 (Colberre-Garapin et al., 1981, J. Mol. Biol.150:1); and hygromycin phosphotransferase (hyg), which confersresistance to hygromycin (Santerre et al., 1984, Gene 30:147). Otherselectable markers, such as but not limited to histidinol and Zeocin™can also be used.

4.2.2 Production of Recombinant Proteins

4.2.2.1 Peptide Tagging

Generating a fusion protein comprising a peptide tag and an animaliatRNA splicing endonuclease subunit can aid the purification of theanimalia tRNA splicing endonuclease subunit. In a preferred embodiment,the animalia tRNA splicing endonuclease subunit is a mammalian tRNAsplicing endonuclease subunit. In a more preferred embodiment, theanimalia tRNA splicing endonuclease is a human animalia tRNA splicingendonuclease subunit. A fusion protein comprising a peptide and ananimalia tRNA splicing endonuclease subunit can be made by ligating thenucleotide sequence encoding the animalia tRNA splicing endonucleasesubunit to the sequence encoding the peptide tag in the proper readingframe. Care should be taken to ensure that the modified gene remainswithin the same translational reading frame, uninterrupted bytranslational stop signals and/or spurious messenger RNA splicingsignals.

The peptide tag may be fused to the amino terminal or to the carboxylterminal of an animalia tRNA splicing endonuclease subunit. The precisesite at which the fusion is made is not critical. The optimal site canbe determined by routine experimentation.

A variety of peptide tags known in the art may be conjugated to ananimalia tRNA splicing endonuclease subunit including, but not limitedto the immunoglobulin constant regions, polyhistidine sequence (Petty,1996, Metal-chelate affinity chromatography, in Current Protocols inMolecular Biology, Vol. 2, Ed. Ausubel et al., Greene Publish. Assoc. &Wiley Interscience), glutathione S-transferase (GST; Smith, 1993,Methods Mol. Cell Bio. 4:220-229), the E. coli maltose binding protein(Guan et al., 1987, Gene 67:21-30), various cellulose binding domains(U.S. Pat. Nos. 5,496,934; 5,202,247; 5,137,819; Tomme et al., 1994,Protein Eng. 7: 117-123), and the FLAG epitope (Short Protocols inMolecular Biology, 1999, Ed. Ausubel et al., John Wiley & Sons, Inc.,Unit 10.11). Other peptide tags that are well-known to one of skill inthe art that are recognized by specific binding partners and thusfacilitate isolation by affinity binding to the binding partner (whichis preferably immobilized and/or on a solid support) may be conjugatedto an animalia tRNA splicing endonuclease subunit. As will beappreciated by those skilled in the art, many methods can be used toobtain the coding region of the above-mentioned peptide tags, includingbut not limited to, DNA cloning, DNA amplification, and syntheticmethods. Some of the peptide tags and reagents for their detection andisolation are available commercially.

In a specific embodiment, the polyhistidine tag conjugated to ananimalia tRNA splicing endonuclease subunit has at least 6, at least 8,at least 10 or at least 10 histidines. In a preferred embodiment, thepolyhistidine tag conjugated to an animalia tRNA splicing endonucleasesubunit has 8 histidines.

In another embodiment, an animalia tRNA splicing endonuclease subunitcan be labeled with more than one peptide. In a specific embodiment, ananimalia tRNA splicing endonuclease subunit is labeled with a peptidetag consisting of 8 histidines and a Flag epitope tag.

In certain embodiments of the invention, different subunits of ananimalia tRNA splicing endonuclease can be conjugated to differentpeptide tags.

4.2.2.2 Expression Systems and Host Cells

Preferred mammalian host cells include but are not limited to thosederived from humans, monkeys and rodents, (see, for example, Kriegler M.in “Gene Transfer and Expression: A Laboratory Manual”, New York,Freeman & Co. 1990), such as monkey kidney cell line transformed by SV40(COS-7, ATCC Accession No. CRL 1651); human embryonic kidney cell lines(293, 293-EBNA, or 293 cells subcloned for growth in suspension culture,Graham et al., J. Gen. Virol., 36:59, 1977; baby hamster kidney cells(BHK, ATCC Accession No. CCL 10); chinese hamster ovary-cells-DHFR(CHO,Urlaub and Chasin. Proc. Natl. Acad. Sci. 77; 4216, 1980); mouse sertolicells (Mather, Biol. Reprod. 23:243-251, 1980); mouse fibroblast cells(NIH-3T3), monkey kidney cells (CVI ATCC Accession No. CCL 70); africangreen monkey kidney cells (VERO-76, ATCC Accession No. CRL-1587); humancervical carcinoma cells (HELA, ATCC Accession No. CCL 2); canine kidneycells (MDCK, ATCC Accession No. CCL 34); buffalo rat liver cells (BRL3A, ATCC Accession No. CRL 1442); human lung cells (W138, ATCC AccessionNo. CCL 75); human liver cells (Hep G2, HB 8065); and mouse mammarytumor cells (MMT 060562, ATCC Accession No. CCL51).

A number of viral-based expression systems may also be utilized withmammalian cells to produce an animalia tRNA splicing endonucleasesubunit. Vectors using DNA virus backbones have been derived from simianvirus 40 (SV40) (Hamer et al., 1979, Cell 17:725), adenovirus (Van Dorenet al., 1984, Mol Cell Biol 4:1653), adeno-associated virus (McLaughlinet al., 1988, J Virol 62:1963), and bovine papillomas virus (Zinn etal., 1982, Proc Natl Acad Sci 79:4897). In cases where an adenovirus isused as an expression vector, the donor DNA sequence may be ligated toan adenovirus transcription/translation control complex, e.g., the latepromoter and tripartite leader sequence. This chimeric gene may then beinserted in the adenovirus genome by in vitro or in vivo recombination.Insertion in a non-essential region of the viral genome (e.g., region E1or E3) will result in a recombinant virus that is viable and capable ofexpressing heterologous products in infected hosts. (See e.g., Logan andShenk, 1984, Proc. Natl. Acad. Sci. (USA) 81:3655-3659).

Other useful eukaryotic host-vector system may include yeast and insectsystems. In yeast, a number of vectors containing constitutive orinducible promoters may be used with Saccharomyces cerevisiae (baker'syeast), Schizosaccharomyces pombe (fission yeast), Pichia pastoris, andHansenula polymorpha (methylotropic yeasts). For a review see, CurrentProtocols in Molecular Biology, Vol. 2, 1988, Ed. Ausubel et al., GreenePublish. Assoc. & Wiley Interscience, Ch. 13; Grant et al., 1987,Expression and Secretion Vectors for Yeast, in Methods in Enzymology,Eds. Wu & Grossman, 1987, Acad. Press, N.Y., Vol. 153, pp. 516-544;Glover, 1986, DNA Cloning, Vol. II, IRL Press, Wash., D.C., Ch. 3; andBitter, 1987, Heterologous Gene Expression in Yeast, Methods inEnzymology, Eds. Berger & Kimmel, Acad. Press, N.Y., Vol. 152, pp.673-684; and The Molecular Biology of the Yeast Saccharomyces, 1982,Eds. Strathem et al., Cold Spring Harbor Press, Vols. I and II.

In an insect system, Autographa californica nuclear polyhidrosis virus(AcNPV) a baculovirus, can be used as a vector to express the human tRNAsplicing endonuclease subunit in Spodoptera frugiperda cells. Thesequences encoding an animalia tRNA splicing endonuclease subunit may becloned into non-essential regions (for example the polyhedrin gene) ofthe virus and placed under control of an AcNPV promoter (for example thepolyhedrin promoter). These recombinant viruses are then used to infecthost cells in which the inserted DNA is expressed. (See e.g., Smith etal., 1983, J Virol 46:584; Smith, U.S. Pat. No. 4,215,051.)

Any of the cloning and expression vectors described herein may besynthesized and assembled from known DNA sequences by well knowntechniques in the art. The regulatory regions and enhancer elements canbe of a variety of origins, both natural and synthetic. Some vectors andhost cells may be obtained commercially. Non-limiting examples of usefulvectors are described in Appendix 5 of Current Protocols in MolecularBiology, 1988, ed. Ausubel et al., Greene Publish. Assoc. & WileyInterscience, which is incorporated herein by reference; and thecatalogs of commercial suppliers such as Clontech Laboratories,Stratagene Inc., and Invitrogen, Inc.

Expression constructs containing a cloned nucleotide sequence encodingan animalia tRNA splicing endonuclease subunit can be introduced intothe host cell by a variety of techniques known in the art, including butnot limited to, for prokaryotic cells, bacterial transformation(Hanahan, 1985, in DNA Cloning, A Practical Approach, 1:109-136), andfor eukaryotic cells, calcium phosphate mediated transfection (Wigler etal., 1977, Cell 11:223-232), liposome-mediated transfection(Schaefer-Ridder et al., 1982, Science 215:166-168), electroporation(Wolff et al., 1987, Proc Natl Acad Sci 84:3344), and microinjection(Cappechi, 1980, Cell 22:479-488).

For long term, high yield production of a properly processed animaliatRNA splicing endonuclease subunit, stable expression in mammalian cellsis preferred. Cell lines that stably express an animalia tRNA splicingendonuclease subunit may be engineered by using a vector that contains aselectable marker. By way of example but not limitation, following theintroduction of the expression constructs, engineered cells may beallowed to grow for 1-2 days in an enriched media, and then are switchedto a selective media. The selectable marker in the expression constructconfers resistance to the selection and optimally allows cells to stablyintegrate the expression construct into their chromosomes and to grow inculture and to be expanded into cell lines. Such cells can be culturedfor a long period of time while an animalia tRNA splicing endonucleasesubunit is expressed continuously.

In a preferred embodiment, an animalia human tRNA splicing endonucleasesubunit is transfected stably in 293T cells (ATCC Accession No.CRL-11268).

4.2.2.3 Protein Purification

Generally, an animalia tRNA splicing endonuclease subunit or theanimalia tRNA splicing endonulcease can be recovered and purified fromrecombinant cell cultures by known methods, including ammonium sulfateprecipitation, acid extraction, anion or cation exchange chromatography,phosphocellulose chromatography, immunoaffinity chromatography,hydroxyapatite chromatography, and lectin chromatography. In a preferredembodiment, the animalia tRNA splicing endonuclease subunit or animaliatRNA splicing endonuclease is a mammalian tRNA splicing endonucleasesubunit or a mammalian tRNA splicing endonuclease, respectively. In amore preferred embodiment, the animalia tRNA splicing endonucleasesubunit or animalia tRNA splicing endonuclease is a human tRNA splicingendonuclease subunit or a human tRNA splicing endonuclease,respectively. Before the animalia tRNA splicing endonuclease subunit canbe purified, total protein has to be prepared from the cell culture.This procedure comprises collection, washing and lysis of said cells andis well known to the skilled artisan.

In particular, a recombinant animalia tRNA splicing endonuclease subunitfused to a peptide tag may be purified based on the properties of thepeptide tag. One approach is based on specific molecular interactionsbetween a tag and its binding partner. The other approach relies on theimmunospecific binding of an antibody to an epitope present on the tagor on the protein which is to be purified. The principle of affinitychromatography well known in the art is generally applicable to both ofthese approaches. Once the animalia tRNA splicing endonucleasesubunit-peptide tag fusion protein is eluted, fractions can be collectedand tested for the presence of the animalia tRNA splicing endonucleaseand/or for the presence of the peptide tag. In a specific embodiment,the fractions are tested for tRNA splicing endonuclease activity.Subsequently, the fractions with tRNA splicing endonuclease activitylevels over a certain threshold level can be pooled.

Described below are several methods based on specific molecularinteractions of a tag and its binding partner.

A method that is generally applicable to purifying an animalia tRNAsplicing endonuclease subunit that are fused to the constant regions ofimmunoglobulin is protein A affinity chromatography, a technique that iswell known in the art. Staphylococcus protein A is a 42 kD polypeptidethat binds specifically to a region located between the second and thirdconstant regions of heavy chain immunoglobulins. Because of the Fcdomains of different classes, subclasses and species of immunoglobulins,affinity of protein A for human Fc regions is strong, but may vary amongspecies. Subclasses that are less preferred include human IgG-3, andmost rat subclasses. For certain subclasses, protein G (of Streptococci)may be used in place of protein A in the purification. Protein-Asepharose (Pharmacia or Biorad) is a commonly used solid phase foraffinity purification of antibodies, and can be used essentially in thesame manner for the purification of an animalia tRNA splicingendonuclease subunit fused to an immunoglobulin Fc fragment. Boundanimalia tRNA splicing endonuclease subunit-Fc fusion protein can beeluted by various buffer systems known in the art, including asuccession of citrate, acetate and glycine-HCl buffers which graduallylowers the pH. This method is less preferred if the recombinant cellsalso produce antibodies which will be co-purified with the human tRNAsplicing endonuclease subunit. See, for example, Langone, 1982, J.Immunol. meth. 51:3; Wilchek et al., 1982, Biochem. Intl. 4:629;Sjobring et al., 1991, J. Biol. Chem. 26:399; page 617-618, inAntibodies A Laboratory Manual, edited by Harlow and Lane, Cold SpringHarbor laboratory, 1988.

Alternatively, a polyhistidine tag may be used, in which case, ananimalia tRNA splicing endonuclease subunit can be purified by metalchelate chromatography. The polyhistidine tag, usually a sequence of sixhistidines, has a high affinity for divalent metal ions, such as nickelions (Ni²⁺), which can be immobilized on a solid phase, such asnitrilotriacetic acid-matrices. Polyhistidine has a well characterizedaffinity for Ni²⁺-NTA-agarose, and can be eluted with either of two mildtreatments: imidazole (0.1-0.2 M) will effectively compete with theresin for binding sites; or lowering the pH just below 6.0 willprotonate the histidine sidechains and disrupt the binding. Thepurification method comprises loading the cell culture lysate onto theNi²⁺-NTA-agarose column, washing the contaminants through, and elutingthe animalia tRNA splicing endonuclease subunit with imidazole or weakacid. Ni²⁺-NTA-agarose can be obtained from commercial suppliers such asSigma (St. Louis) and Qiagen. Antibodies that recognize thepolyhistidine tag are also available which can be used to detect andquantitate the human tRNA splicing endonuclease subunit.

Another exemplary peptide tag that can be used is theglutathione-S-transferase (GST) sequence, originally cloned from thehelminth, Schistosoma japonicum. In general, an animalia tRNA splicingendonuclease subunit-GST fusion protein expressed in a prokaryotic hostcell, such as E. coli, can be purified from the cell culture lysate byabsorption with glutathione agarose beads, followed by elution in thepresence of free reduced glutathione at neutral pH. Since GST is knownto form dimers under certain conditions, dimeric animalia tRNA splicingendonuclease subunit may be obtained. See, Smith, 1993, Methods Mol.Cell Bio. 4:220-229.

Another useful peptide tag that can be used is the maltose bindingprotein (MBP) of E. coli, which is encoded by the malE gene. An animaliatRNA splicing endonuclease subunit fused to MBP binds to amylose resinwhile contaminants are washed away. The bound animalia tRNA splicingendonuclease subunit-MBP fusion is eluted from the amylose resin bymaltose. See, for example, Guan et al., 1987, Gene 67:21-30.

The second approach for purifying an animalia tRNA splicing endonucleasesubunit or animalia tRNA splicing endonuclease is applicable to peptidetags that contain an epitope for which polyclonal or monoclonalantibodies are available. It is also applicable if polyclonal ormonoclonal antibodies specific to an animalia tRNA splicing endonucleasesubunit or the animalia tRNA splicing endonuclease are available.Various methods known in the art for purification of protein byimmunospecific binding, such as immunoaffinity chromatography, andimmunoprecipitation, can be used. See, for example, Chapter 13 inAntibodies A Laboratory Manual, edited by Harlow and Lane, Cold SpringHarbor laboratory, 1988; and Chapter 8, Sections I and II, in CurrentProtocols in Immunology, ed. by Coligan et al., John Wiley, 1991; thedisclosure of which are both incorporated by reference herein.

In particular the invention relates to the expression and purificationof the human tRNA splicing endonuclease subunits Hs Sen2p and Hs Sen34p(see Table 2). TABLE 2 Gene Homolog LocusLink Genbank Protein GenomeContig Hs Sen2p Sc Sen2p 80746 NP_079541 NT_005927.12 Hs Sen34p ScSen34p 79042 XP_085899 NT_011225.9Sc = sacromyces cerivisiaeHs = Human

Oligonucleotides complementary to the 5′ and 3′ ends of the open readingframes of the animalia tRNA splicing endonuclease subunits can be usedto PCR amplify the open reading frames encoding the animalia tRNAsplicing endonuclease.

The invention also relates to the expression and purification of an HsSen 2p variant (“Hs Sen 2 var.”). The Hs Sen 2 var. is a splice variantof Hs Sen2 lacking exon 8 of the genomic DNA sequence for Human Sen 2.FIG. 2 depicts an amino acid sequence alignment of the amino acidsequences of the two human Sen 2 subunits (i.e., Hs Sen2 and Hs Sen 2var.) and the amino acid sequence of the yeast subunit Sc Sen 2p. Thesequence alignment reveals a high degree of similarity in the YRGGYmotif (SEQ ID NO: 4), the active site for the 5′ splice site of yeast(Sc Sen 2p) and archael (not shown) tRNA splicing endonuclease. Basedupon the sequence alignment, the Hs Sen 2 var. lacks the putativetransmembrane domain found in the Hs Sen 2 endonuclease, which mayaffect the localization of the Hs Sen2 var. in an animalia cell.

In specific embodiments, the Hs Sen2 var. catalyzes the endonucleolyticcleavage of substrates other than those containing tRNA introns. Inother embodiments, the Hs Sen2 var. catalyzes the endonucleolyticcleavage of substrates containing tRNA introns. In yet otherembodiments, the Hs Sen2 var. catalyzes the endonucleolytic cleavage ofsubstrates containing tRNA introns and substrates that do not containtRNA introns.

The human subunits, including, but not limited to, Hs Sen2, Hs Sen2 var.and Hs Sen 34, can be utilized in accordance with the methods of theinvention. In a specific embodiment, the Hs Sen 2 subunit is utilized inaccordance with the methods of the invention. In another embodiment, theHs Sen 2 var. subunit is utilized in accordance with the methods of theinvention. In another embodiment, the Hs Sen 34 subunit is utilized inaccordance with the methods of the invention. In yet another embodiment,Hs Sen 2, Hs Sen 2 var., Hs Sen 34 or any combination thereof isutilized in accordance with the methods of the invention.

4.2.2.4 Expression and Purification of Fungal tRNA Splicing Endonuclease

Fungal tRNA splicing endonuclease subunits (in particular, the yeasttRNA splicing endonuclease subunits) and the fungal tRNA splicingendonuclease (in particular, yeast tRNA splicing endonuclease) can beexpressed and purified by any method known to the skilled artisan. Afungal tRNA splicing endonuclease subunit or the fungal tRNA splicingendonuclease can be purified by the methods discussed above for ananimalia tRNA splicing endonuclease subunit or the animalia tRNAsplicing endonuclease. In a specific embodiment, yeast tRNA splicingendonuclease or a subunit thereof is purified according to the proceduredescribed in Trotta et al., 1997, Cell 89:849-858.

4.3 Compounds

Libraries screened using the methods of the present invention cancomprise a variety of types of compounds. Examples of libraries that canbe screened in accordance with the methods of the invention include, butare not limited to, peptoids; random biooligomers; diversomers such ashydantoins, benzodiazepines and dipeptides; vinylogous polypeptides;nonpeptidal peptidomimetics; oligocarbamates; peptidyl phosphonates;peptide nucleic acid libraries; antibody libraries; carbohydratelibraries; and small molecule libraries (preferably, small organicmolecule libraries). In some embodiments, the compounds in the librariesscreened are nucleic acid or peptide molecules. In a non-limitingexample, peptide molecules can exist in a phage display library. Inother embodiments, the types of compounds include, but are not limitedto, peptide analogs including peptides comprising non-naturallyoccurring amino acids, e.g., D-amino acids, phosphorous analogs of aminoacids, such as α-amino phosphoric acids and α-amino phosphoric acids, oramino acids having non-peptide linkages, nucleic acid analogs such asphosphorothioates and PNAs, hormones, antigens, synthetic or naturallyoccurring drugs, opiates, dopamine, serotonin, catecholamines, thrombin,acetylcholine, prostaglandins, organic molecules, pheromones, adenosine,sucrose, glucose, lactose and galactose. Libraries of polypeptides orproteins can also be used in the assays of the invention.

In a preferred embodiment, the combinatorial libraries are small organicmolecule libraries including, but not limited to, benzodiazepines,isoprenoids, thiazolidinones, metathiazanones, pyrrolidines, morpholinocompounds, and benzodiazepines. In another embodiment, the combinatoriallibraries comprise peptoids; random bio-oligomers; benzodiazepines;diversomers such as hydantoins, benzodiazepines and dipeptides;vinylogous polypeptides; nonpeptidal peptidomimetics; oligocarbamates;peptidyl phosphonates; peptide nucleic acid libraries; antibodylibraries; or carbohydrate libraries. Combinatorial libraries arethemselves commercially available (see, e.g., ComGenex, Princeton, N.J.;Asinex, Moscow, Ru, Tripos, Inc., St. Louis, Mo.; ChemStar, Ltd, Moscow,Russia; 3D Pharmaceuticals, Exton, Pa.; Martek Biosciences, Columbia,Md.; etc.).

In a preferred embodiment, the library is preselected so that thecompounds of the library are more amenable for cellular uptake. Forexample, compounds are selected based on specific parameters such as,but not limited to, size, lipophilicity, hydrophilicity, and hydrogenbonding, which enhance the likelihood of compounds getting into thecells. In another embodiment, the compounds are analyzed bythree-dimensional or four-dimensional computer computation programs.

The combinatorial compound library for use in accordance with themethods of the present invention may be synthesized. There is a greatinterest in synthetic methods directed toward the creation of largecollections of small organic compounds, or libraries, which could bescreened for pharmacological, biological or other activity. Thesynthetic methods applied to create vast combinatorial libraries areperformed in solution or in the solid phase, i.e., on a solid support.Solid-phase synthesis makes it easier to conduct multi-step reactionsand to drive reactions to completion with high yields because excessreagents can be easily added and washed away after each reaction step.Solid-phase combinatorial synthesis also tends to improve isolation,purification and screening. However, the more traditional solution phasechemistry supports a wider variety of organic reactions than solid-phasechemistry.

Combinatorial compound libraries of the present invention may besynthesized using the apparatus described in U.S. Pat. No. 6,190,619 toKilcoin et al., which is hereby incorporated by reference in itsentirety. U.S. Pat. No. 6,190,619 discloses a synthesis apparatuscapable of holding a plurality of reaction vessels for parallelsynthesis of multiple discrete compounds or for combinatorial librariesof compounds.

In one embodiment, the combinatorial compound library can be synthesizedin solution. The method disclosed in U.S. Pat. No. 6,194,612 to Boger etal., which is hereby incorporated by reference in its entirety, featurescompounds useful as templates for solution phase synthesis ofcombinatorial libraries. The template is designed to permit reactionproducts to be easily purified from unreacted reactants usingliquid/liquid or solid/liquid extractions. The compounds produced bycombinatorial synthesis using the template will preferably be smallorganic molecules. Some compounds in the library may mimic the effectsof non-peptides or peptides. In contrast to solid phase synthesize ofcombinatorial compound libraries, liquid phase synthesis does notrequire the use of specialized protocols for monitoring the individualsteps of a multistep solid phase synthesis (Egner et al., 1995, J. Org.Chem. 60:2652; Anderson et al., 1995, J. Org. Chem. 60:2650; Fitch etal., 1994, J. Org. Chem. 59:7955; Look et al., 1994, J. Org. Chem.49:7588; Metzger et al., 1993, Angew. Chem., Int. Ed. Engl. 32:894;Youngquist et al., 1994, Rapid Commun. Mass Spect. 8:77; Chu et al.,1995, J. Am. Chem. Soc. 117:5419; Brummel et al., 1994, Science 264:399;and Stevanovic et al., 1993, Bioorg. Med. Chem. Lett. 3:431).

Combinatorial compound libraries useful for the methods of the presentinvention can be synthesized on solid supports. In one embodiment, asplit synthesis method, a protocol of separating and mixing solidsupports during the synthesis, is used to synthesize a library ofcompounds on solid supports (see e.g., Lam et al., 1997, Chem. Rev.97:41-448; Ohlmeyer et al., 1993, Proc. Natl. Acad. Sci. USA90:10922-10926 and references cited therein). Each solid support in thefinal library has substantially one type of compound attached to itssurface. Other methods for synthesizing combinatorial libraries on solidsupports, wherein one product is attached to each support, will be knownto those of skill in the art (see, e.g., Nefzi et al., 1997, Chem. Rev.97:449-472).

As used herein, the term “solid support” is not limited to a specifictype of solid support. Rather a large number of supports are availableand are known to one skilled in the art. Solid supports include silicagels, resins, derivatized plastic films, glass beads, cotton, plasticbeads, polystyrene beads, alumina gels, and polysaccharides. A suitablesolid support may be selected on the basis of desired end use andsuitability for various synthetic protocols. For example, for peptidesynthesis, a solid support can be a resin such asp-methylbenzhydrylamine (pMBHA) resin (Peptides International,Louisville, Ky.), polystyrenes (e.g., PAM-resin obtained from BachemInc., Peninsula Laboratories, etc.), including chloromethylpolystyrene,hydroxymethylpolystyrene and aminomethylpolystyrene,poly(dimethylacrylamide)-grafted styrene co-divinyl-benzene (e.g.,POLYHIPE resin, obtained from Aminotech, Canada), polyamide resin(obtained from Peninsula Laboratories), polystyrene resin grafted withpolyethylene glycol (e.g., TENTAGEL or ARGOGEL, Bayer, Tubingen,Germany) polydimethylacrylamide resin (obtained from Milligen/Biosearch,California), or Sepharose Pharmacia, Sweden).

In some embodiments of the present invention, compounds can be attachedto solid supports via linkers. Linkers can be integral and part of thesolid support, or they may be nonintegral that are either synthesized onthe solid support or attached thereto after synthesis. Linkers areuseful not only for providing points of compound attachment to the solidsupport, but also for allowing different groups of molecules to becleaved from the solid support under different conditions, depending onthe nature of the linker. For example, linkers can be, inter alia,electrophilically cleaved, nucleophilically cleaved, photocleavable,enzymatically cleaved, cleaved by metals, cleaved under reductiveconditions or cleaved under oxidative conditions. In a preferredembodiment, the compounds are cleaved from the solid support prior tohigh throughput screening of the compounds.

In certain embodiments of the invention, the compound is a smallmolecule.

4.4 In Vitro Screening Assays

Various in vitro assays can be used to identify and verify the abilityof a compound to modulate the activity of an animalia tRNA splicingendonuclease. Multiple in vitro assays can be performed simultaneouslyor sequentially to assess the affect of a compound on the activity of ananimalia tRNA splicing endonuclease. In a preferred embodiment, the invitro assays described herein are performed in a high throughput format.In another preferred embodiment, the animalia tRNA splicing endonucleaseutilized in the assays described herein is a mammalian tRNA splicingendonuclease and more preferably, a human tRNA splicing endonuclease.

4.4.1 Reporter Gene-Based Assays

4.4.1.1 Cell-Based Assays

After a vector containing the reporter gene construct is transformed ortransfected into a host cell and a compound library is synthesized orpurchased or both, the cells are used to screen the library to identifycompounds that modulate the activity of an animalia tRNA splicingendonuclease. The reporter gene-based assays may be conducted bycontacting a compound or a member of a library of compounds with a cellgenetically engineered to contain a reporter gene construct comprising areporter gene and a tRNA intron within the open reading frame of thereporter gene, or within the 5′ untranslated region, 3′ untranslatedregion or both the 5′ and 3′ untranslated regions of the reporter geneconstruct, or within a mRNA splice site of the reporter gene; andmeasuring the expression of said reporter gene. The alteration inreporter gene expression relative to a previously determined referencerange, the absence of the compound or a control in such reporter-genebased assays indicates that a particular compound modulates the activityof an animalia tRNA splicing endonuclease. A decrease in reporter geneexpression relative to a previously determined reference range, theabsence of the compound or a control in such reporter-gene based assaysindicates that a particular compound reduces or inhibits the activity ofan animalia tRNA splicing endonuclease (e.g., the recognition orcleavage of a tRNA intron). An increase in reporter gene expressionrelative to a previously determined reference range, the absence of thecompound or a control in such reporter-gene based assays indicates thata particular compound enhances the activity of an animalia tRNA splicingendonuclease. In a preferred embodiment, a negative control (e.g., PBSor another agent that is known to have no effect on the expression ofthe reporter gene) and a positive control (e.g., an agent that is knownto have an effect on the expression of the reporter gene, preferably anagent that effects the activity of an animalia tRNA splicingendonuclease) are included in the cell-based assays described herein.

The step of contacting a compound or a member of a library of compoundswith an animalia cell genetically engineered to contain a reporter geneconstruct comprising a reporter gene and a tRNA intron within the openreading frame of the reporter gene, within the 5′ untranslated region,3′ untranslated region or both the 5′ and 3′ untranslated regions of thereporter gene construct or within a mRNA splice site may be conductedunder physiologic conditions. In specific embodiment, a compound or amember of a library of compounds is added to the cells in the presenceof an aqueous solution. In accordance with this embodiment, the aqueoussolution may comprise a buffer and a combination of salts, preferablyapproximating or mimicking physiologic conditions. Alternatively, theaqueous solution may comprise a buffer, a combination of salts, and adetergent or a surfactant. Examples of salts which may be used in theaqueous solution include, but not limited to, KCl, NaCl, and/or MgCl₂.The optimal concentration of each salt used in the aqueous solution isdependent on the cells and compounds used and can be determined usingroutine experimentation. The step of contacting a compound or a memberof a library of compounds with an animalia cell genetically engineeredto contain the reporter gene construct may be performed for at least 0.2hours, 0.25 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5hours, 6 hours, 8 hours, 10 hours, 12 hours, 18 hours, or at least 1day.

In one embodiment, the invention provides a method for identifying acompound that modulates animalia tRNA splicing endonuclease activity,said method comprising: (a) expressing a nucleic acid comprising areporter gene in a cell, wherein the reporter gene comprises a tRNAintron; (b) contacting said cell with a member of a library ofcompounds; and (c) detecting the expression of said reporter gene,wherein a compound that modulates tRNA splicing endonuclease activity isidentified if the expression of said reporter gene in the presence of acompound is altered relative to a previously determined reference rangeor the expression of said reporter gene in the absence of the compoundor the presence of a control. In another embodiment, the inventionprovides a method for identifying a compound that modulates animaliatRNA splicing endonuclease activity, said method comprising: (a)contacting a member of a library of compounds with a cell containing anucleic acid comprising a reporter gene, wherein the reporter genecomprises a tRNA intron; and (b) detecting the expression of saidreporter gene, wherein a compound that modulates tRNA splicingendonuclease activity is identified if the expression of said reportergene in the presence of a compound is altered relative to a previouslydetermined reference range the expression of said reporter gene in theabsence of said compound or the presence of a control.

The expression of a reporter gene and/or activity of the protein encodedby the reporter gene in the cell-based reporter-gene assays may bedetected by any technique well-known to one of skill in the art. Theexpression of a reporter gene can be readily detected, e.g., byquantifying the protein and/or RNA encoded by said gene. Many methodsstandard in the art can be thus employed, including, but not limited to,immunoassays to detect and/or visualize gene expression (e.g., Westernblot, immunoprecipitation followed by sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE), immunocytochemistry, etc)and/or hybridization assays to detect gene expression by detectingand/or visualizing respectively mRNA encoding a gene (e.g., Northernassays, dot blots, in situ hybridization, etc), etc. Such assays areroutine and well known in the art (see, e.g., Ausubel et al, eds, 1994,Current Protocols in Molecular Biology, Vol. 1, John Wiley & Sons, Inc.,New York, which is incorporated by reference herein in its entirety).Exemplary immunoassays are described briefly below (but are not intendedby way of limitation).

Immunoprecipitation protocols generally comprise lysing a population ofcells in a lysis buffer such as RIPA buffer (1% NP-40 or Triton X-100,1% sodium deoxycholate, 0.1% SDS, 0.15 M NaCl, 0.01 M sodium phosphateat pH 7.2, 1% Trasylol) supplemented with protein phosphatase and/orprotease inhibitors (e.g., EDTA, PMSF, aprotinin, sodium vanadate),adding the antibody which recognizes the antigen to the cell lysate,incubating for a period of time (e.g., 1 to 4 hours) at 40° C., addingprotein A and/or protein G sepharose beads to the cell lysate,incubating for about an hour or more at 40° C., washing the beads inlysis buffer and resuspending the beads in SDS/sample buffer. Theability of the antibody to immunoprecipitate a particular antigen can beassessed by, e.g., western blot analysis. One of skill in the art wouldbe knowledgeable as to the parameters that can be modified to increasethe binding of the antibody to an antigen and decrease the background(e.g., pre-clearing the cell lysate with sepharose beads). For furtherdiscussion regarding immunoprecipitation protocols see, e.g., Ausubel etal, eds, 1994, Current Protocols in Molecular Biology, Vol. 1, JohnWiley & Sons, Inc., New York at 10.16.1.

Western blot analysis generally comprises preparing protein samples,electrophoresis of the protein samples in a polyacrylamide gel (e.g.,8%-20% SDS-PAGE depending on the molecular weight of the antigen),transferring the protein sample from the polyacrylamide gel to amembrane such as nitrocellulose, PVDF or nylon, blocking the membrane inblocking solution (e.g. PBS with 3% BSA or non-fat milk), washing themembrane in washing buffer (e.g. PBS-Tween 20), blocking the membranewith primary antibody (the antibody which recognizes the antigen)diluted in blocking buffer, washing the membrane in washing buffer,blocking the membrane with a secondary antibody (which recognizes theprimary antibody, e.g. an anti-human antibody) conjugated to anenzymatic substrate (e.g., horseradish peroxidase or alkalinephosphatase) or radioactive molecule (e.g., ³²P or ¹²⁵I) diluted inblocking buffer, washing the membrane in wash buffer, and detecting thepresence of the antigen. One of skill in the art would be knowledgeableas to the parameters that can be modified to increase the signaldetected and to reduce the background noise. For further discussionregarding western blot protocols see, e.g., Ausubel et al, eds, 1994,Current Protocols in Molecular Biology, Vol. 1, John Wiley & Sons, Inc.,New York at 10.8.1.

ELISAs comprise preparing antigen, coating the well of a 96 wellmicrotiter plate with the antigen, adding a primary antibody (whichrecognizes the antigen) conjugated to a detectable compound such as anenzymatic substrate (e.g., horseradish peroxidase or alkalinephosphatase) to the well and incubating for a period of time, anddetecting the presence of the antigen. In ELISAs the antibody ofinterest does not have to be conjugated to a detectable compound;instead, a second antibody (which recognizes the primary antibody)conjugated to a detectable compound may be added to the well. Further,instead of coating the well with the antigen, the antibody may be coatedto the well. In this case, a second antibody conjugated to a detectablecompound may be added following the addition of the antigen of interestto the coated well. One of skill in the art would be knowledgeable as tothe parameters that can be modified to increase the signal detected aswell as other variations of ELISAs known in the art. For furtherdiscussion regarding ELISAs see, e.g., Ausubel et al, eds, 1994, CurrentProtocols in Molecular Biology, Vol. 1, John Wiley & Sons, Inc., NewYork at 11.2.1.

Methods for detecting the activity of a protein encoded by a reportergene will vary with the reporter gene used. Assays for the variousreporter genes are well-known to one of skill in the art. For example,as described in Section 5.2.1., luciferase, beta-galactosidase(“beta-gal”), beta-glucoronidase (“GUS”), beta-lactamase,chloramphenicol acetyltransferase (“CAT”), and alkaline phosphatase(“AP”) are enzymes that can be analyzed in the presence of a substrateand could be amenable to high throughput screening. For example, thereaction products of luciferase, beta-galactosidase (“beta-gal”), andalkaline phosphatase (“AP”) are assayed by changes in light imaging(e.g., luciferase), spectrophotometric absorbance (e.g., beta-gal), orfluorescence (e.g., AP). Assays for changes in light output, absorbance,and/or fluorescence are easily adapted for high throughput screening.For example, beta-gal activity can be measured with a microplate reader.Green fluorescent protein (“GFP”) activity can be measured by changes influorescence. For example, in the case of mutant GFPs that fluoresce at488 nm, standard fluorescence activated cell sorting (“FACS”) equipmentcan be used to separate cells based upon GFP activity.

Alterations in the expression of a reporter gene may be determined bycomparing the level of expression of the reporter gene to a negativecontrol (e.g., PBS or another agent that is known to have no effect onthe expression of the reporter gene) and optionally, a positive control(e.g., an agent that is known to have an effect on the expression of thereporter gene, preferably an agent that effects the activity of ananimalia tRNA splicing endonuclease). Alternatively, alterations in theexpression of a reporter gene may be determined by comparing the levelof expression of the reporter gene to a previously determined referencerange.

4.4.1.2 Cell-Free Assays

After a vector containing the reporter gene construct is produced, acell-free translation extract is generated or purchased, and a compoundlibrary is synthesized or purchased or both, the cell-free translationextract and nucleic acid are used to screen the library to identifycompounds that modulate the activity of an animalia tRNA splicingendonuclease. The reporter gene-based assays may be conducted in acell-free manner by contacting a compound with a cell-free extract and areporter gene construct comprising a reporter gene and a tRNA intronwithin the open reading frame of the reporter gene or within the 5′untranslated region, 3′ untranslated region or both the 5′ and 3′untranslated regions of the reporter gene construct, or in a mRNAsplicing site of the reporter gene, and measuring the expression of saidreporter gene. The alteration in reporter gene expression relative to apreviously determined reference range, the absence of the compound or acontrol in such reporter-gene based assays indicates that a particularcompound modulates the activity of an animalia tRNA splicingendonuclease. A decrease in reporter gene expression relative to apreviously determined reference range, the absence of the compound or acontrol in such reporter-gene based assays indicates that a particularcompound reduces or inhibits the activity of an animalia tRNA splicingendonuclease (e.g., the recognition or cleavage of a tRNA intron). Anincrease in reporter gene expression relative to a previously determinedreference range, the absence of the compound or a control in suchreporter-gene based assays indicates that a particular compound enhancesthe activity of an animalia tRNA splicing endonuclease. In a preferredembodiment, a negative control (e.g. PBS or another agent that is knownto have no effect on the expression of the reporter gene) and a positivecontrol (e.g., an agent that is known to have an effect on theexpression of the reporter gene, preferably an agent that effects theactivity of an animalia tRNA splicing endonuclease) are included in thecell-free assays described herein.

In a specific embodiment, the invention provides a method foridentifying a compound that modulates animalia tRNA splicingendonuclease activity, said method comprising: (a) contacting a memberof a library of compounds with a cell-free extract and a nucleic acidcomprising a reporter gene, wherein the reporter gene comprises a tRNAintron; and (b) detecting the expression of said reporter gene, whereina compound that modulates tRNA splicing endonuclease activity isidentified if the expression of said reporter gene in the presence of acompound is altered relative to the expression of said reporter gene inthe absence of said compound or the presence of a control.

The activity of a compound in the cell-free extract can be determined byassaying the activity of a reporter protein encoded by a reporter gene,or alternatively, by quantifying the expression of the reporter gene by,for example, labeling the in vitro translated protein (e.g., with³⁵S-labeled methionine), northern blot analysis, RT-PCR or byimmunological methods, such as western blot analysis orimmunoprecipitation. Such methods are well-known to one of skill in theart.

4.4.2 FRET Assays

Fluorescence resonance energy transfer (“FRET”) can be used to detectalterations in the activity of an animalia tRNA splicing endonuclease.In the FRET assays described herein, the subunits of an animalia tRNAsplicing endonuclease or a substrate for an animalia tRNA splicingendonuclease may be labeled with fluorophores. In circumstances where asubunit(s) of an animalia tRNA splicing endonuclease has not beendetermined or isolated, the substrate for the animalia tRNA splicingendonuclease is labeled with fluorophores.

In order to obtain FRET between the fluorescent donor moiety and thefluorescent acceptor moiety or a quencher, the two moieties have to bein spatial proximity with each other. Thus, in certain embodiments, asubstrate for an animalia tRNA splicing endonuclease is labeled suchthat the fluorescent donor moiety and the fluorescent acceptor moiety ora quencher are at most 0.5 nm, at most 1 nm, at most 5 nm, at most 10nm, at most 20 nm, at most 30 nm, at most 40 nm, at most 50 nm or atmost 100 nm apart from each other.

In certain embodiments, the substrates depicted in FIG. 1 are used inthe FRET assays. In particular, the hybridized tRNA substrate andcircularly permuted tRNA substrate depicted in FIGS. 1B and 1C,respectively, are used in the FRET assays. The free 5′ and 3′ ends ofthe intron of the hybridized tRNA substrate (FIG. 1B) or the free 5′ and3′ ends of the intron of circularly permuted tRNA substrate (FIG. 1C)may be labeled with a fluorophore such that the close spatial proximityof the fluorophore on the 5′ end with the fluorophore on the 3′ endresults in fluorescence resonance energy transfer. Cleavage of thesubstrate will then result in a spatial separation of the labeled 5′ endfrom the labeled 3′ end and thus, in reduced fluorescence resonanceenergy transfer. Thus, the skilled artisan can measure FRET anddetermine the concentration of cleaved versus uncleaved substrate. Theconcentration of uncleaved substrate decreases as FRET declines.

Alternatively, the 3′ end or the 5′ end is labeled with a fluorophoreand the other end, i.e., the 5′ end or the 3′ end, respectively, islabeled with a quencher of the fluorophore. Upon cleavage of the intronby tRNA splicing endonculease, the quencher and the fluorophore areseparated from each other resulting in a measurable change influorescence. The fluorescence signal increases as the cleavage reactionproceeds.

4.4.2.1 Cell-Based Assays with a Labeled Substrate

The FRET cell-based assays may be conducted by microinjecting ortransfecting (e.g., using liposomes or electroporation) a substrate foran animalia tRNA splicing endonuclease into a cell and contacting thecell with a compound, wherein the substrate is labeled at the 5′ endwith a fluorophore and labeled at the 3′ end with a quencher, oralternatively, the substrate is labeled at the 5′ end with a quencehrand labeled at the 3′ end with a fluorophore, and measuring thefluorescence of the substrate by, e.g., fluorescence microscopy or afluorescence emission detector such as a Viewlux or Analyst. Theendogenous tRNA splicing endonuclease will cleave the substrate andresult in the production of a detectable fluorescent signal. A compoundthat inhibits or reduces the activity of the endogenous tRNA splicingendonuclease will inhibit or reduce the cleavage of the substrate andthus, inhibit or reduce the production of a detectable fluorescentsignal relative to a negative control (e.g., PBS). A compound thatenhances the activity of the endogenous endonuclease will enhance thecleavage of the substrate and thus, increase the production of adetectable fluorescent signal relative to a negative control (e.g.,PBS).

Alternatively, the FRET cell-based assays may be conducted bymicroinjecting or transfecting a substrate for an animalia tRNA splicingendonuclease into a cell and contacting the cell with a compound,wherein the substrate is labeled at the 5′ end with a fluorescent donormoiety and labeled at the 3′ end with a fluorescent acceptor moiety, or,alternatively, the substrate is labeled at the 5′ end with a fluorescentacceptor moiety and labeled at the 3′ end with a fluorescent donormoiety, and measuring the fluorescence of the substrate by, e.g.,fluorescence microscopy or a fluorescence emission detector such as aViewlux or Analyst. The endogenous tRNA splicing endonuclease willcleave the substrate and result in the production of a detectablefluorescent signal by the fluorescent donor moiety and fluorescentacceptor moiety at the wavelength of the fluorescent donor moiety. Acompound that inhibits or reduces the activity of the endogenous tRNAsplicing endonuclease will inhibit or reduce cleavage of the substrateand thus, increase the fluorescence emission of the fluorescent acceptormoiety at the wavelength of the fluorescent donor moiety relative to anegative control (e.g., PBS). A compound that enhances the activity ofthe endogenous tRNA splicing endonuclease will enhance the cleavage ofthe substrate and thus, reduce the fluorescence emission of thefluorescent acceptor moiety at the wavelength of the fluorescent donormoiety relative to a negative control (e.g., PBS). In a preferredembodiment, a negative control (e.g. PBS or another agent that is knownto have no effect on the cleavage of the substrate) and a positivecontrol (e.g., an agent that is known to have an effect on the cleavageof the substrate) are included in the FRET cell-based assays describedherein.

Optionally, an agent that inhibits or reduces the activity of theanimalia tRNA splicing ligase such as an antibody that specificallybinds to the ligase may be used in the contacting step to determine,ensure or confirm that a compound is not solely functioning byinhibiting or reducing the activity of the ligase. Alternatively, theFRET cell-based assay may be conducted in cells deficient in tRNAsplicing ligase. As another alternative, ATP may be excluded from theassay. Without being bound by theory, since ATP is required for the tRNAsplicing ligase reaction, any effect a compound has in the assay shouldbe attributable to an effect of the compound on the endonuclease.

The assay can be conducted in any buffer system that provides conditionsconducive to the tRNA endonuclease reaction. Such buffer systems arewell known to the skilled artisan. In a specific embodiment, the bufferis the medium in which the cell culture is kept. Care should be takenthat Magnesium ions are present in the medium.

In certain embodiments, the assay is conducted for at least 0.2 hours,0.25 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6hours, 8 hours, 10 hours, 12 hours, 18 hours, or at least 1 day.

In a specific embodiment, the invention provides a method of identifyingan antiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a)microinjecting or transfecting a substrate of a tRNA splicingendonuclease into a animalia cell, wherein the substrate is labeled atthe 5′ end with a fluorophore and labeled at the 3′ end with a quencher,or alternatively, the substrate is labeled at the 5′ end with a quencehrand labeled at the 3′ end with a fluorophore; (b) contacting the cellwith a member of a library of compounds; and (c) measuring the activityof the tRNA splicing endonuclease, wherein an antiproliferative compoundthat inhibits or reduces tRNA splicing activity is identified if afluorescent signal is not detectable in the presence of the compoundrelative to the absence of the compound or the presence of a control. Inanother embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a) contactingan animalia cell containing a substrate of a tRNA splicing endonucleasewith a member of a library of compounds, wherein the substrate islabeled at the 5′ end with a fluorophore and at the 3′ end with aquencher, or alternatively, the substrate is labeled at the 5′ end witha quencehr and labeled at the 3′ end with a fluorophore; and (b)measuring the activity of the tRNA splicing endonuclease, wherein anantiproliferative compound that inhibits or reduces tRNA splicingactivity is identified if a fluorescent signal is not detectable in thepresence of the compound relative to the absence of the compound or thepresence of a control.

In another embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a)microinjecting or transfecting a substrate of a tRNA splicingendonuclease into a animalia cell, wherein the substrate is labeled atthe 5′ end with a fluorescent donor moiety and labeled at the 3′ endwith a fluorescent acceptor moiety, or alternatively, the substrate islabeled at the 5′ end with a fluorescent acceptor moiety and labeled atthe 3′ end with a fluorescent donor moiety; (b) contacting the cell witha member of a library of compounds; and (c) measuring the activity ofthe tRNA splicing endonuclease, wherein an antiproliferative compoundthat inhibits or reduces tRNA splicing activity is identified if thefluorescent signal detected in the presence of the compound is alteredrelative to the absence of the compound or the presence of a control. Inanother embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a) contactingan animalia cell containing substrate of a tRNA splicing endonucleasewith a member of a library of compounds, wherein the substrate islabeled at the 5′ end with a fluorescent donor moiety and labeled at the3′ end with a fluorescent acceptor moiety, or alternatively, thesubstrate is labeled at the 5′ end with a fluorescent acceptor moietyand labeled at the 3′ end with a fluorescent donor moiety; and (b)measuring the activity of the tRNA splicing endonuclease, wherein anantiproliferative compound that inhibits or reduces tRNA splicingactivity is identified if the fluorescence emission of the fluorescentacceptor moiety at the wavelength of the fluorescent donor moiety in thepresence of the compound is reducred relative to the absence of thecompound or the presence of a control.

Any nucleotide sequence recognized and excised by an animalia tRNAsplicing endonuclease may be utilized as a substrate for an animaliatRNA splicing endonuclease in a FRET assay described herein. Forexample, a nucleotide sequence comprising a bulge-helix-bulge structureor a mature domain of a precursor tRNA may be utilized as a substratefor an animalia tRNA splicing endonuclease in a FRET assay describedherein. A nucleotide sequence recognized and excised by an animalia tRNAsplicing endonuclease may comprise 10 nucleotides, 15 nucleotides, 20nucleotides, 25 nucleotides, 25 nucleotides, 30 nucleotides, 40nucleotides, 45 nucleotides, 50 nucleotides, 55 nucleotides, 60nucleotides, 65 nucleotides, 75 nucleotides, 100 nucleotides, 125nucleotides, 150 nucleotides, or more. In a specific embodiment, thesubstrates for a tRNA splicing endonuclease utilized in the FRET assaysdescribed herein comprise a tRNA intron. The substrate may comprise abulge-helix-bulge conformation. In a preferred embodiment, the substratecomprises a tRNA mature domain that contains an intron.

In accordance with the invention, a single pair of fluorescent donor andacceptor moieties. The substrate can be labeled with different pairs offluorescent donor moieties and fluorescent acceptor moieties. Forexample, two, three, four, five or more pairs of fluorescent donormoieties and fluorescent acceptor moieties can be used. In thissituation, preferably, at least one of the pairs comprise a fluorescentacceptor moiety that has a different emission spectrum from thefluorescent acceptor moiety of at least one of the other pairs.Alternatively, when at least three pairs are used, the fluorescentacceptor moiety of the first pair, second pair and third pair has adifferent emission spectrum than the fluorescent acceptor moiety of theother two. Methods for labeling the substrate with a fluorescentacceptor moiety, a fluorescent donor moiety and/or quencher arewell-known in the art (see, e.g., U.S. Pat. Nos. 6,472,156, 6,451,543,6,348,322, 6,342,379, 6,323,039, 6,297,018, 6,291,201, 6,280,981,5,843,658, and 5,439,797, the disclosures of which are incorporated byreference in their entirety). The labeled substrate can be microinjectedor transfected into animalia cells (preferably, mammalian cells and morepreferably, human cells) utilizing techniques well-known to one of skillin the art (see, e.g., Adams et al., 1991, Nature 349:694-697).

The activity of a compound on an animalia tRNA splicing endonuclease inthe FRET cell-based assays can be determined by measuring thefluorescent emission spectra of the substrate utilizing techniqueswell-known to one of skill in the art. The fluorescent emission spectrameasured depends, in part, on the fluorophore used.

4.4.2.2 Cell-Free Assays with a Labeled Substrate

The FRET cell-free assays may be conducted by contacting a substrate foran animalia tRNA splicing endonuclease with a cell-free extract (seeSection 4.4.1.2 supra regarding cell-free extracts, preferably, a tRNAsplicing endonuclease extract) or a purified animalia tRNA splicingendonuclease and a compound, wherein the substrate is labeled at the 5′end with a fluorophore and labeled at the 3′ end with a quencher or,alternatively, the the substrate is labeled at the 3′ end with afluorophore and labeled at the 5′ end with a quencher, and measuring thefluorescence of the substrate in, e.g., a fluorescence emission detectorsuch as a Viewlux or Analyst. The tRNA splicing endonuclease in thecell-free extract will cleave the substrate and result in the productionof a detectable fluorescent signal. A compound that inhibits or reducesthe activity of the tRNA splicing endonuclease will inhibit or reducethe cleavage of the substrate and thus, inhibit or reduce the productionof a detectable fluorescent signal relative to a negative control (e.g.,PBS). A compound that enhances the activity of the tRNA splicingendonuclease will enhance the cleavage of the substrate and thus,increase the production of a detectable signal relative to a negativecontrol (e.g., PBS).

Alternatively, the FRET cell-free-based assays may be conducted bycontacting a substrate for an animalia tRNA splicing endonuclease with acell-free extract (preferably, a tRNA splicing endonuclease extract) ora purified animalia tRNA splicing endonuclease and a compound, whereinthe substrate is labeled at the 5′ end with a fluorescent donor moietyand labeled at the 3′ end with a fluorescent acceptor moiety, oralternatively, the substrate is labeled at the 5′ end with a fluorescentacceptor moiety and labeled at the 3′ end with a fluorescent donormoiety, and measuring the fluorescence of the substrate by, e.g., afluorescence emission detector such as a Viewlux or Analyst. The tRNAsplicing endonuclease will cleave the substrate and result in theproduction of a detectable fluorescent signal by the fluorescent donormoiety and fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety. A compound that inhibits or reduces theactivity of the tRNA splicing endonuclease will inhibit or reducecleavage of the substrate and thus, increase the fluorescence emissionof the fluorescent acceptor moiety at the wavelength of the fluorescentdonor moiety relative to a negative control (e.g., PBS). A compound thatenhances the activity of the tRNA splicing endonuclease will enhance thecleavage of the substrate and thus, reduce the fluorescence emission ofthe fluorescent acceptor moiety at the wavelength of the fluorescentdonor moiety relative to a negative control (e.g., PBS). In a preferredembodiment, a negative control (e.g. PBS or another agent that is knownto have no effect on the cleavage of the substrate) and a positivecontrol (e.g., an agent that is known to have an effect on the cleavageof the substrate) are included in the FRET cell-free assays describedherein.

The assay can be conducted in any buffer system that provides conditionsconducive to the tRNA endonuclease reaction. Such buffer systems arewell known to the skilled artisan. In a specific embodiment, the buffercomprises 20 mM Tris at a pH of 7.0, 50 mM KCl, 0.11 nM DTT, 5 mM MgCl₂,and 0.4% Triton X100. Care should be taken that pH, salt concentration,detergent concentration etc. of the buffer system do not interfere withFRET.

In certain embodiments, the assay is conducted for at least 0.2 hours,0.25 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6hours, 8 hours, 10 hours, 12 hours, 18 hours, or at least 1 day.

In one embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a) contactingan animalia cell-free extract (preferably, a tRNA splicing endonucleaseextract) or a purified animalia tRNA splicing endonuclease with asubstrate of a tRNA splicing endonuclease and a member of a library ofcompounds, wherein the substrate is labeled at the 5′ end with afluorophore and labeled at the 3′ end with a quencher, or alternatively,the substrate is labeled at the 5′ end with a quencher and labeled atthe 3′ end with a fluorophore; and (b) measuring the activity of thetRNA splicing endonuclease, wherein an antiproliferative compound thatinhibits or reduces tRNA splicing activity is identified if afluorescent signal is not detectable in the presence of the compoundrelative to the absence of the compound or the presence of a control. Inanother embodiment, the invention provides a method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a) contactingan animalia cell-free extract (preferably, a tRNA splicing endonucleaseextract) or a purified animalia tRNA splicing endonuclease with asubstrate of a tRNA splicing endonuclease and a member of a library ofcompounds, wherein said substrate is labeled at the 5′ end with afluorescent donor moiety and labeled at the 3′ end with a fluorescentacceptor moiety, or alternatively, the substrate is labeled at the 5′end with a fluorescent acceptor moiety and labeled at the 3′ end with afluorescent donor moiety; and (b) measuring the activity of the tRNAsplicing endonuclease, wherein an antiproliferative compound thatinhibits tRNA splicing activity is identified if the fluorescenceemission of the fluorescent acceptor moiety at the wavelength of thefluroescent donor moiety detected in the presence of the compound isdecreased relative to the absence of the compound or the presence of acontrol.

In accordance with the invention, the substrate can be labeled with asingle pair of fluorescent donor and acceptor moieties. The substratecan be labeled with different pairs of fluorescent donor moieties andfluorescent acceptor moieties. For example, two, three, four, five ormore pairs of fluorescent donor moieties and fluorescent acceptormoieties can be used. In this situation, preferably, at least one of thepairs comprise a fluorescent acceptor moiety that has a differentemission spectrum from the fluorescent acceptor moiety of at least oneof the other pairs. Alternatively, when at least three pairs are used,the fluorescent acceptor moiety of the first pair, second pair and thirdpair has a different emission spectrum than the fluorescent acceptormoiety of the other two. Methods for labeling the substrate with afluorescent acceptor moiety, a fluorescent donor moiety and/or quencherare well-known in the art (see, e.g., U.S. Pat. Nos. 6,472,156,6,451,543, 6,348,322, 6,342,379, 6,323,039, 6,297,018, 6,291,201,6,280,981, 5,843,658, and 5,439,797, the disclosures of which areincorporated by reference in their entirety).

The activity of a compound on an animalia tRNA splicing endonuclease inthe FRET cell-free assays can be determined by measuring the fluorescentemission spectra of the substrate utilizing techniques well-known to oneof skill in the art. The fluorescent emission spectra measured depends,in part, on the fluorophore used.

4.4.2.3 Cell-Based Assays with Labeled Enzyme

A FRET cell-based assay may be conducted by microinjecting ortransfecting a first subunit of an animalia tRNA splicing endonuclease(e.g., SEN2) labeled with a fluorophore and a second, different subunitof an animalia tRNA splicing endonuclease (e.g., SEN34) labeled with aquencher into a cell and contacting the cell with a compound, andmeasuring the fluorescence of the animalia tRNA splicing endonucleaseby, e.g. fluorescence microscopy or a fluorescence emission detectorsuch as a Viewlux or Analyst. Preferably, the cell microinjected ortransfected is deficient in one or more of the subunits of the animaliatRNA splicing endonuclease. Any methods known to the skilled artisan canbe used to remove the expression and/or function of one or more subunitsof the animalia tRNA splicing endonuclease from the cell. In a specificembodiment, RNAi is used to transiently remove one or more of thesubunits of the animalia tRNA splicing endonuclease. The formation ofthe animalia tRNA splicing endonuclease from the labeled subunits willresult in a reduction in the fluorescence detectable. A compound thatinhibits or reduces the formation of the animalia tRNA splicingendonuclease will reduce or inhibit the production of a detectablefluorescent signal relative to a negative control (e.g., PBS). Acompound that enhances the formation of the animalia tRNA splicingendonuclease will increase the fluorescence detectable relative to anegative control (e.g., PBS).

Alternatively, a FRET cell-based assay may be conducted bymicroinjecting a first subunit of an animalia tRNA splicing endonuclease(e.g., SEN2) labeled with a fluorescent donor moiety and a second,different subunit of an animalia tRNA splicing endonuclease (e.g.,SEN34) labeled with a fluorescent acceptor moiety into a cell andcontacting the cell with a compound, and measuring the fluorescence ofthe animalia tRNA splicing endonuclease by, e.g., fluorescencemicroscopy or a fluorescence emission detector such as a Viewlux orAnalyst. The formation of the animalia tRNA splicing endonuclease willresult in the production of a detectable fluorescent signal by thefluorescent donor moiety and fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety. A compound that inhibits orreduces the formation of the animalia tRNA splicing endonuclease willreduce the fluorescence emission of the fluorescent acceptor moiety atthe wavelength of the fluorescent donor moiety relative to a negativecontrol (e.g., PBS). A compound that enhances the formation of theanimalia tRNA splicing endonuclease will increase the fluorescenceemission of the fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety relative to a negative control (e.g. PBS). In apreferred embodiment, a negative control (e.g., PBS or another agentthat is known to have no effect on the cleavage of the substrate) and apositive control (e.g., an agent that is known to have an effect on thecleavage of the substrate) are included in the FRET cell-based assaysdescribed herein.

In certain embodiments, the compound and the cell are incubated for atleast 0.2 hours, 0.25 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, 18 hours, or atleast 1 day.

Methods for labeling a subunit of an animalia tRNA splicing endonucleasewith a fluorescent acceptor moiety, a fluorescent donor moiety and/orquencher are well-known in the art (see, e.g., U.S. Pat. Nos. 6,472,156,6,451,543, 6,348,322, 6,342,379, 6,323,039, 6,297,018, 6,291,201,6,280,981, 5,843,658, and 5,439,797, the disclosures of which areincorporated by reference in their entirety).

4.4.2.4 Cell-Free Assays with Labeled Enzyme

A FRET cell-free assay may be conducted by contacting a first subunit ofan animalia tRNA splicing endonuclease (e.g., SEN2) labeled with afluorophore and a second subunit of an animalia tRNA splicingendonuclease (e.g., SEN34) labeled with a quencher with a compound invitro under conditions conducive to the formation of the endonuclease,and measuring the fluorescence of the animalia tRNA splicingendonuclease by, e.g., a fluorescence emission detector such as aViewlux or Analyst. The formation of the animalia tRNA splicingendonuclease from the labeled subunits will result in a reduction in thefluorescence detectable. A compound that inhibits or reduces theformation of the animalia tRNA splicing endonuclease will enhance theproduction of detectable fluorescent signal relative to the absence ofthe compound or the presence of a negative control (e.g., PBS). Acompound that enhances the formation of the animalia tRNA splicingendonuclease will reduce or inhibit the fluorescence detectable relativeto the absence of the compound or a negative control (e.g., PBS).

Alternatively, a FRET cell-free assay may be conducted by contacting afirst subunit of an animalia tRNA splicing endonuclease (e.g., SEN2)labeled with a fluorescent donor moiety and a second, different subunitof an animalia tRNA splicing endonuclease (e.g., SEN34) labeled with afluorescent acceptor moiety with a compound in vitro under conditionsconducive to the formation of the endonuclease, and measuring thefluorescence of the animalia tRNA splicing endonuclease by, e.g., afluorescence emission detector such as a Viewlux or Analyst. Theformation of the animalia tRNA splicing endonuclease will result in theproduction of a detectable fluorescent signal by the fluorescent donormoiety and fluorescent acceptor moiety at the wavelength of thefluorescent donor. A compound that inhibits or reduces the formation ofthe animalia tRNA splicing endonuclease will reduce the fluorescenceemission of the fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety relative to the absence of the compound or thepresence of a negative control (e.g., PBS). A compound that enhances theformation of the animalia tRNA splicing endonuclease will increase thefluorescence emission of the fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety relative to the absence ofthe compound or the presence of a negative control (e.g., PBS). In apreferred embodiment, a negative control (e.g., PBS or another agentthat is known to have no effect on the cleavage of the substrate) and apositive control (e.g. an agent that is known to have an effect on thecleavage of the substrate) are included in the FRET cell-free assaysdescribed herein.

4.4.3 Direct Binding Assays

Compounds that modulate the activity of an animalia tRNA splicingendonuclease can be identified by direct binding assays. In particular,compounds that inhibit the activity of an animalia tRNA splicingendonuclease by directly or indirectly reducing or inhibiting theinteraction between a substrate for an animalia tRNA splicingendonuclease and an animalia tRNA splicing endonuclease. Such assays aredescribed in International Patent Publication Nos. WO 02/083837 and WO02/083953, the disclosures of which are hereby incorporated by referencein their entireties. Briefly, direct binding assays may be conducted byattaching a library of compounds to solid supports, e.g., polymer beads,with each solid support having substantially one type of compoundattached to its surface. The plurality of solid supports of the libraryis exposed in aqueous solution to a substrate for an animalia tRNAsplicing endonuclease having a detectable label, forming a dye-labeledsubstrate:support-attached compound complex. Binding of a substrate to aparticular compound labels the solid support, e.g., bead, comprising thecompound, which can be physically separated from other, unlabeled solidsupports. Once labeled solid supports are identified, the chemicalstructures of the compounds thereon can be determined by, e.g., readinga code on the solid support that correlates with the structure of theattached compound.

Alternatively, direct binding assays may be conducted by contacting asubstrate for an animalia tRNA splicing endonuclease having a detectablelabel with a member of a library of compounds free in solution, inlabeled tubes or microtiter wells, or a microarray. Compounds in thelibrary that bind to the labeled substrate of an animalia tRNA splicingendonuclease will form a detectably labeled complex that can beidentified and removed from the uncomplexed, unlabeled compounds in thelibrary, and from uncomplexed, labeled substrate of an animalia tRNAsplicing endonuclease, by a variety of methods including, but notlimited to, methods that differentiate changes in the electrophoretic,chromatographic, or thermostable properties of the complexed substrate.

4.4.4 Fluorescence Polarization Assay

The effect of a compound on the activity of an animalia tRNA splicingendonuclease may be determined utilizing a fluorescencepolarization-based assay. In such an assay, a fluorescently labeledsubstrate for an animalia tRNA splicing endonuclease is contacted withan animalia cell-free extract (preferably, an animalia tRNA splicingendonuclease extract) or a purified animalia tRNA splicing endonucleaseand a compound or a member of a library of compounds; and thefluorescently polarized light emitted is measured. An important aspectof this assay is that the size of the substrate used in the assay islarge enough to distinguish a change in fluorescent polarized lightemitted following cleavage of the substrate. The tRNA splicingendonuclease in the cell-free extract or the purified animalia tRNAsplicing endonuclease will cleave the substrate and result in a changein intensity of emitted polarized light. Fluorescently labeledsubstrates when excited with plane polarized light will emit light in afixed plane only if they do not rotate during the period betweenexcitation and emission. The extent of depolarization of the emittedlight depends upon the amount of rotation of the substrate, which isdependent on the size of the substrate. Small substrates rotate morethan larger substrates between the time they are excited and the timethey emit fluorescent light. A small fluorescently labeled substraterotates rapidly and the emitted light is depolarized. A largefluorescently labeled substrate rotates more slowly and results in theemitted light remaining polarized. A compound that inhibits the activityof the tRNA splicing endonuclease will inhibit or reduce the cleavage ofthe substrate and thus, decrease the rotation of the substrate relativeto a negative control (e.g., PBS) or the absence of the compound, whichwill result in the emitted light remaining polarized. A compound thatenhances the activity of the tRNA splicing endonuclease will enhance thecleavage of the substrate and thus, increase the rotation of thesubstrate relative to a negative control (e.g., PBS) or the absence ofthe compound, which will result in more of the emitted light beingdepolarized.

The intensities of the light are measured in planes 90° apart and aremany times designated the horizontal and vertical intensities. In someinstruments the excitation filter is moveable while the emission filteris fixed. In certain other machines the horizontal and verticalintensities are measured simultaneously via fiber optics. Research gradefluorescence polarization instruments are commercially available from,e.g., Pan Vera, BMG Lab Technologies, and LJL Biosystems. Abott providesclinical laboratory instrumentation. The value of fluorescencepolarization is determined by the following equation:${polarization} = \frac{{intensity}_{vertical} - {intensity}_{horizontal}}{{intensity}_{vertical} + {{intensity}_{horizontal}.}}$

Fluorescence polarization values are most often divided by 1000 andexpressed as millipolarization units (mP).

In a specific embodiment, the hybridized tRNA or circularly permutedtRNA depicted in FIG. 1 are used as a substrate for the endonuclease. Inaccordance with this embodiment, the 5′ end in the intron of thehybridized tRNA or the circularly permuted tRNA, or the 3′ end in theintron of the hybridized tRNA or the circularly permuted tRNA or bothare labeled with a fluorophore. Upon cleavage, the size of the moleculeto which the fluorophore is attached changes because the intron isreleased from the substrate. The decrease in molecular weight of thelabeled molecule results in an increase of depolarization of light thatis emitted from the fluorophore. Measuring the amount of depolarizationallows the skilled artisan to determine the amount of cleaved substrate.

4.4.5 tRNA Endonuclease Suppression Assay

The effect of a compound or a member of a library of compoundson theactivity of an animalia tRNA splicing endonuclease may be determinedusing a tRNA endonuclease suppression assay. In such an assay, a hostcell is engineered to contain a first reporter gene construct and asuppressor tRNA; the expression of the suppressor tRNA is induced; thehost cell is contacted with a compound or a member of a library ofcompounds; and the expression of the reporter gene and/or the activityof the protein encoded by the reporter gene is measured. The firstreporter gene construct comprises a reporter gene with a nonsense codonin its open reading frame such that the open reading frame isinterrupted. Standard mutagenesis techniques described, e.g., inSambrook (Sambrook, 1989, Molecular Cloning, A Laboratory Manual, SecondEdition; DNA Cloning, Volumes I and II (Glover, Ed. 1985)) may be usedto introduce a nonsense codon into the open reading frame of anyreporter gene well-known to one of skill in the art. The first reportergene construct is transfected into a host cell engineered to contain asuppressor tRNA. Alternatively, the first reporter gene is cotransfectedinto a host cell with a suppressor tRNA. The suppressor tRNA'sexpression is regulated by a controllable regulatory element; such as bya tetracycline regulated regulatory element (see, e.g. Buvoli et al,2000, Molecular and Cellular Biology 20:3116-3124; Park and Bhandary,1998, Molecular and Cellular Biology 18:4418-4425) and the suppressortRNA contains a tRNA intron in the anticodon stem such that onlyproperly spliced suppressor tRNA is functional. Expression of functionalsuppressor tRNA is dependent on (i) the transcription of the suppressortRNA, and (ii) tRNA splicing. The expression of functional suppressortRNA suppresses the nonsense codon in the reporter gene and results infull length, functional reporter gene expression. Accordingly, theexpression of full length, functional reporter gene correlates with theexpression of functional suppressor tRNA, which in turn correlates withthe level of transcription of the suppressor tRNA and tRNA splicing. Theexpression of full-length reporter gene and the activity of the proteinencoded by the reporter gene can be assayed by any method well known tothe skilled artisan or as described herein.

A compound that inhibits or reduces the activity of an animalia tRNAsplicing endonuclease will inhibit or reduce the production offunctional suppressor tRNA and thus, reduce the expression of thereporter gene relative to a previously determined reference range or acontrol. A compound that enhances the activity of an animalia tRNAsplicing endonuclease will enhance the production of functionalsuppressor tRNA and thus, enhance the production of the reporter generelative to a previously determined reference range or a control.

The step of inducing the expression of the suppressor tRNA may beconducted simultaneously with the step of contacting the host cell witha compound or at least 5 minutes, at least 15 minutes, at least 0.5hours, at least 1 hour, at least 1.5 hours, at least 2 hours, at least 3hours, at least 4 hours, at least 5 hours, at least 6 hours, at least 8hours, at least 10 hours or at least 12 hours before the step ofcontacting the compound with the host cell. In certain embodiments, theexpression of the suppressor tRNA is induced by incubating the host cellwith an agent such as, e.g., tetracycline, for approximately 5 minutes,approximately 15 minutes, approximately 0.5 hours, approximately 1 hour,approximately 1.5 hours, approximately 2 hours, approximately 3 hours,approximately 4 hours, approximately 5 hours, 6 approximately hours, 8approximately hours, approximately 10 hours or approximately 12 hours.In other embodiments, the host cell is contacted with the compound forapproximately 5 minutes, approximately 15 minutes, approximately 0.5hours, approximately 1 hour, approximately 1.5 hours, approximately 2hours, approximately 3 hours, approximately 4 hours, approximately 5hours, 6 approximately hours, 8 approximately hours, approximately 10hours or approximately 12 hours.

Optionally, the host cell is engineered to contain a second reportergene construct comprising a reporter gene different from the firstreporter gene that does not contain a nonsense codon. In a specificembodiment, the reporter genes used in the tRNA endonuclease suppressionassay are Red and Green Click Beetle luciferase, wherein the Redluciferase contains the nonsense codon. A host cell may be engineered tostably express the two luciferase genes and the suppressor tRNA whoseexpression is regulated by a controlled regulatory element (such as atetracycline controlled regulatory element). In the absence of an agentsuch as tetracycline, the suppressor tRNA is not expressed and thus thered-to-green ratio is low. In the presence of an agent such astetracycline, the suppressor tRNA is expressed and thus the red-to-greenratio increases. For a high throughput screening, cells are plated inthe presence of a compound. After a certain time-period media containingan agent such as tetracycline is added to induce suppressor tRNAexpression.

Compounds that inhibit tRNA splicing endonuclease will decrease thered-to-green ration compared to a control without the compound. Oncecompounds are identified in this assay that modulate the activity ofanimalia tRNA splicing endonuclease, they may be tested using, one ormore of the assays described above to confirm their activity.

4.4.6 FISH Assay

The activity of an animalia tRNA splicing endonuclease may be determinedin an assay in which the persistence and quantity of tRNA intron isdetected in an animalia cell. The amount of tRNA intron is quantified atdifferent time points after or during the incubation of the cell withthe compound. The tRNA intron can be detected by means of Fluorescencein situ hybridization (FISH) using a tRNA intron-specific probe. Incertain embodiments, a control experiment is conducted in parallelwherein the animalia cell is not contacted with a compound.

In the absence of an inhibitor of animalia tRNA splicing endonuclease,the splicing reaction is fast and the concentration of intron in thecell is low. Without being bound by theory, because the spliced intronis normally degraded the concentration of tRNA intron in the animaliacell is below the detection threshold. In the presence of an inhibitorof animalia tRNA splicing endonuclease, the splicing reaction is sloweddown and the amount of tRNA intron increases. Thus, a compound thatinhibits animalia tRNA splicing endonuclease can be identified by itsability to increase the level of tRNA intron in the animalia cell.

Methods for conducting FISH are well-known to the skilled artisan andcan be used with the invention. Exemplary methods for FISH are describedin Sarkar and Hopper, 1998 (Mol. Biol. Cell 9:3041-3055), which isincorporated herein in its entirety.

In certain embodiments, a FISH assay is used to determine the effect ofa compound on the activity of an animalia tRNA splicing endonuclease ina high-throughput screen. In particular a 96-lens microscope can be usedfor a high-throughput screen based on FISH. In a specific embodiment, 96cell cultures are incubated in a 96-well plate with different compounds.Subsequently, the cells are subjected to a FISH analysis using a tRNAintron specific probe and analyzed using the 96-lens microscope. Thepresence of a signal or the presence of a significantly stronger signaldemonstrates that tRNA intron was present in the cells at elevatedlevels and thus the compound is a candidate inhibitor of tRNA splicingendonuclease.

Without being bound by theory, the FISH assay identifies the compound asinhibitor of the tRNA splicing endonuclease directly. Thus, in certainembodiments, a compound that was identified in a FISH assay as aninhibitor of tRNA splicing is a prima facie candidate for an inhibitorof tRNA splicing endonuclease.

4.4.7 Other Screening Assays

The activity of an animalia tRNA splicing endonuclease may be determinedin an assay in which the amount of substrate for a tRNA splicingendonuclease cleaved by the endonuclease in the presence of a compoundrelative to a control (preferably, a negative control and morepreferably, a negative control and a positive control) is detected. Suchan assay may be conducted by contacting or incubating a compound with alabeled substrate for an animalia tRNA splicing endonuclease and acell-free extract or purified animalia tRNA splicing endonuclease underconditions conducive for tRNA splicing endonuclease activity, andmeasuring the amount of cleaved substrate. The substrate for theanimalia tRNA splicing endonuclease can be labeled with any detectableagent. Useful labels in the present invention can include, but are notlimited to, spectroscopic labels such as fluorescent dyes (e.g.,fluorescein and derivatives such as fluorescein isothiocyanate (FITC)and Oregon Green™, rhodamine and derivatives (e.g., Texas red,tetramethylrhodimine isothiocynate (TRITC), bora-3a,4a-diaza-s-indacene(BODIPY®) and derivatives, etc.), digoxigenin, biotin, phycoerythrin,AMCA, CyDye™, and the like), radiolabels (e.g., ³H, ¹²⁵I, ³⁵S, ¹⁴C, ³²P,³³P, etc.), enzymes (e.g., horse radish peroxidase, alkaline phosphataseetc.), spectroscopic colorimetric labels such as colloidal gold orcolored glass or plastic (e.g., polystyrene, polypropylene, latex, etc.)beads, or nanoparticles—nanoclusters of inorganic ions with defineddimension from 0.1 to 1000 nm) utilizing techniques known to one ofskill in the art.

For example, a substrate of an animalia tRNA splicing endonuclease canbe labeled by any method known to the skilled artisan. In certainembodiments, a substrate of an animalia tRNA splicing endonuclease canbe labeled using site-specific labeling of RNA with fluorophores. Inmore specific embodiments, a substrate of an animalia tRNA splicingendonuclease is labeled using the methods described in Qin and Pyle,1999 (Methods 18(1):60-70), which is incorporated in its entiretyherein. The optimal method for labeling of a substrate of an animaliatRNA splicing endonuclease can be determined by the skilled artisanusing routine experimentation. In a specific embodiment, a substrate ofan animalia tRNA splicing endonuclease is labeled using differentmethods, different labels and/or different positions in the tRNAsubstrate for labeling. The differently labeled substrates are thensubjected separately to a splicing assay in the presence and absence,respectively of an inhibitor or an activator of an animalia tRNAsplicing endonuclease. The optimal label for the screening assays is thelabel that allows for the most easily detectable and most reproducibledetection of the effect of the inhibitor or the activater. Otherlabeling procedures, however, may also be used that, for example,provide other desirable advantages.

In certain embodiments, a compound is contacted or incubated with alabeled substrate for an animalia tRNA splicing endonuclease and acell-free extract or purified animalia tRNA splicing endonuclease for atleast 5 minutes, at least 10 minutes, at least 15 minutes, at least 30minutes, at least 1 hour, at least 2 hours, or more. The amount ofcleaved substrate is proportional to the activity of the tRNA splicingendonuclease. The amount of cleaved tRNA splicing endonuclease can bemeasured by any technique known to one skilled in the art.

In certain embodiments, the cleaved tRNA splicing endonuclease substrateis separated from the uncleaved tRNA splicing endonuclease substrate bygel-electrophoresis. The amount of cleaved tRNA splicing endonucleasesubstrate can be quantified by measuring the intensity of the signal ofthe cleaved tRNA splicing endonuclease substrate. The stronger thesignal produced by the cleaved tRNA splicing endonuclease substraterelative to the uncleaved tRNA splicing endonuclease substrate the moreactive is the tRNA splicing endonuclease. The signal intensity can bequantified using autoradiography or a phosphoimager. If the activity ofthe tRNA splicing endonuclease is decreased in the presence of acompound, i.e., if the signal of the cleaved tRNA splicing endonucleasesubstrate relative to the uncleaved tRNA splicing endonuclease substrateis decreased compared to the reaction without the compound or in thepresence of a negative control, the compound is identified as aninhibitor of the tRNA splicing endonuclease.

In other embodiments, the amount of cleaved tRNA is determined usingmass spectrometry.

4.5 Characterization of the Structure of Compounds

If the library comprises arrays or microarrays of compounds, whereineach compound has an address or identifier, the compound can bedeconvoluted, e.g. by cross-referencing the positive sample to originalcompound list that was applied to the individual test assays.

If the library is a peptide or nucleic acid library, the sequence of thecompound can be determined by direct sequencing of the peptide ornucleic acid. Such methods are well known to one of skill in the art.

A number of physico-chemical techniques can be used for the de novocharacterization of compounds bound to the target RNA. Examples of suchtechniques include, but are not limited to, mass spectrometry, NMRspectroscopy, X-ray crytallography and vibrational spectroscopy.

4.5.1 Mass Spectrometry

Mass spectrometry (e.g., electrospray ionization (“ESI”),matrix-assisted laser desorption-ionization (“MALDI”), F andourier-transform ion cyclotron resonance (“FT-ICR”) can be used forelucidating the structure of a compound.

MALDI uses a pulsed laser for desorption of the ions and atime-of-flight analyzer, and has been used for the detection ofnoncovalent tRNA:amino-acyl-tRNA synthetase complexes (Gruic-Sovulj etal., 1997, J. Biol. Chem. 272:32084-32091). However, covalentcross-linking between the target nucleic acid and the compound isrequired for detection, since a non-covalently bound complex maydissociate during the MALDI process.

ESI mass spectrometry (“ESI-MS”) has been of greater utility forstudying noncovalent molecular interactions because, unlike the MALDIprocess, ESI-MS generates molecular ions with little to no fragmentation(Xavier et al., 2000, Trends Biotechnol. 18(8):349-3563. ESI-MS has beenused to study the complexes formed by HIV Tat peptide and protein withthe TAR RNA (Sannes-Lowery et al., 1997, Anal. Chem. 69:5130-5135).

Fourier-transform ion cyclotron resonance (“FT-ICR”) mass spectrometryprovides high-resolution spectra, isotope-resolved precursor ionselection, and accurate mass assignments (Xavier et al., 2000, TrendsBiotechnol. 18(8):349-356). FT-ICR has been used to study theinteraction of aminoglycoside antibiotics with cognate and non-cognateRNAs (Hofstadler et al., 1999, Anal. Chem. 71:3436-3440; and Griffey etal., 1999, Proc. Natl. Acad. Sci. USA 96:10129-10133). As true for allof the mass spectrometry methods discussed herein, FT-ICR does notrequire labeling a compound.

An advantage of mass spectroscopy is not only the elucidation of thestructure of the compound, but also the determination of the structureof the compound bound to an RNA. Such information can enable thediscovery of a consensus structure of a compound that specifically bindsto an RNA.

4.5.2 NMR Spectroscopy

NMR spectroscopy is a valuable technique for identifying complexedtarget nucleic acids by qualitatively determining changes in chemicalshift, specifically from distances measured using relaxation effects,and NMR-based approaches have been used in the identification of smallmolecule binders of protein drug targets (Xavier et al., 2000, TrendsBiotechnol. 18(8):349-356). The determination of structure-activityrelationships (“SAR”) by NMR is the first method for NMR described inwhich small molecules that bind adjacent subsites are identified bytwo-dimentional ¹H-¹⁵N spectra of the target protein (Shuker et al.,1996, Science 274:1531-1534). The signal from the bound molecule ismonitored by employing line broadening, transferred NOEs and pulsedfield gradient diffusion measurements (Moore, 1999, Curr. Opin.Biotechnol. 10:54-58). A strategy for lead generation by NMR using alibrary of small molecules has been recently described (Fejzo et al.,1999, Chem. Biol. 6:755-769).

SAR by NMR can be used to elucidate the structure of a compound.

As described above, NMR spectroscopy is a technique for identifyingbinding sites in target nucleic acids by qualitatively determiningchanges in chemical shift, specifically from distances measured usingrelaxation effects. Examples of NMR that can be used for the inventioninclude, but are not limited to, one-dimentional NMR, two-dimentionalNMR, correlation spectroscopy (“COSY”), and nuclear Overhauser effect(“NOE”) spectroscopy. Such methods of structure determination ofcompounds are well-known to one of skill in the art.

Similar to mass spectroscopy, an advantage of NMR is the not only theelucidation of the structure of the compound, but also the determinationof the structure of the compound bound to the RNA. Such information canenable the discovery of a consensus structure of a compound thatspecifically binds to an RNA.

4.53 X Ray Crystallography

X-ray crystallography can be used to elucidate the structure of acompound. For a review of x-ray crystallography see, e.g., Blundell etal. 2002, Nat Rev Drug Discov 1(1):45-54. The first step in x-raycrystallography is the formation of crystals. The formation of crystalsbegins with the preparation of highly purified and soluble samples. Theconditions for crystallization is then determined by optimizing severalsolution variables known to induce nucleation, such as pH, ionicstrength, temperature, and specific concentrations of organic additives,salts and detergent. Techniques for automating the crystallizationprocess have been developed to automate the production of high-qualityprotein crystals. Once crystals have been formed, the crystals areharvested and prepared for data collection. The crystals are thenanalyzed by diffraction (such as multi-circle diffractometers,high-speed CCD detectors, and detector off-set). Generally, multiplecrystals must be screened for structure determinations.

4.5.4 Vibrational Spectroscopy

Vibrational spectroscopy (e.g. infrared (IR) spectroscopy or Ramanspectroscopy) can be used for elucidating the structure of a compound.

Infrared spectroscopy measures the frequencies of infrared light(wavelengths from 100 to 10,000 nm) absorbed by the compound as a resultof excitation of vibrational modes according to quantum mechanicalselection rules which require that absorption of light cause a change inthe electric dipole moment of the molecule. The infrared spectrum of anymolecule is a unique pattern of absorption wavelengths of varyingintensity that can be considered as a molecular fingerprint to identifyany compound.

Infrared spectra can be measured in a scanning mode by measuring theabsorption of individual frequencies of light, produced by a gratingwhich separates frequencies from a mixed-frequency infrared lightsource, by the compound relative to a standard intensity (double-beaminstrument) or pre-measured (‘blank’) intensity (single-beaminstrument). In a preferred embodiment, infrared spectra are measured ina pulsed mode (“FT-IR”) where a mixed beam, produced by aninterferometer, of all infrared light frequencies is passed through orreflected off the compound. The resulting interferogram, which may ormay not be added with the resulting interferograms from subsequentpulses to increase the signal strength while averaging random noise inthe electronic signal, is mathematically transformed into a spectrumusing Fourier Transform or Fast Fourier Transform algorithms.

Raman spectroscopy measures the difference in frequency due toabsorption of infrared frequencies of scattered visible or ultravioletlight relative to the incident beam. The incident monochromatic lightbeam, usually a single laser frequency, is not truly absorbed by thecompound but interacts with the electric field transiently. Most of thelight scattered off the sample will be unchanged (Rayleigh scattering)but a portion of the scatter light will have frequencies that are thesum or difference of the incident and molecular vibrational frequencies.The selection rules for Raman (inelastic) scattering require a change inpolarizability of the molecule. While some vibrational transitions areobservable in both infrared and Raman spectrometry, must are observableonly with one or the other technique. The Raman spectrum of any moleculeis a unique pattern of absorption wavelengths of varying intensity thatcan be considered as a molecular fingerprint to identify any compound.

Raman spectra are measured by submitting monochromatic light to thesample, either passed through or preferably reflected off, filtering theRayleigh scattered light, and detecting the frequency of the Ramanscattered light. An improved Raman spectrometer is described in U.S.Pat. No. 5,786,893 to Fink et al., which is hereby incorporated byreference.

Vibrational microscopy can be measured in a spatially resolved fashionto address single beads by integration of a visible microscope andspectrometer. A microscopic infrared spectrometer is described in U.S.Pat. No. 5,581,085 to Reffner et al., which is hereby incorporated byreference in its entirety. An instrument that simultaneously performs amicroscopic infrared and microscopic Raman analysis on a sample isdescribed in U.S. Pat. No. 5,841,139 to Sostek et al., which is herebyincorporated by reference in its entirety.

In one embodiment of the method, compounds are synthesized onpolystyrene beads doped with chemically modified styrene monomers suchthat each resulting bead has a characteristic pattern of absorptionlines in the vibrational (IR or Raman) spectrum, by methods includingbut not limited to those described by Fenniri et al., 2000, J. Am. Chem.Soc. 123:8151-8152. Using methods of split-pool synthesis familiar toone of skill in the art, the library of compounds is prepared so thatthe spectroscopic pattern of the bead identifies one of the componentsof the compound on the bead. Beads that have been separated according totheir ability to bind target RNA can be identified by their vibrationalspectrum. In one embodiment of the method, appropriate sorting andbinning of the beads during synthesis then allows identification of oneor more further components of the compound on any one bead. In anotherembodiment of the method, partial identification of the compound on abead is possible through use of the spectroscopic pattern of the beadwith or without the aid of further sorting during synthesis, followed bypartial resynthesis of the possible compounds aided by doped beads andappropriate sorting during synthesis.

In another embodiment, the IR or Raman spectra of compounds are examinedwhile the compound is still on a bead, preferably, or after cleavagefrom bead, using methods including but not limited to photochemical,acid, or heat treatment. The compound can be identified by comparison ofthe IR or Raman spectral pattern to spectra previously acquired for eachcompound in the combinatorial library.

4.6 Secondary Assays

The compounds identified in the assays described supra that modulate theactivity of an animalia tRNA splicing endonuclease (for conveniencereferred to herein as a “lead” compound) can be further tested for bothdirect binding to RNA and biological activity. In one embodiment, thecompounds are tested for biological activity in further assays and/oranimal models. In another embodiment, the lead compound is used todesign congeners or analogs. In another embodiment, the lead compound isused to assess the effect on fungal tRNA splicing endonuclease andfungal proliferation. In yet another embodiment, mutagenesis studies canbe conducted to assess the mechanism by which a lead compound ismodulating the activity of an animalia tRNA splicing endonuclease.

4.6.1 Phenotypic or Physiological Readout

The compounds identified in the assays described supra (for conveniencereferred to herein as a “lead” compound) can be tested for biologicalactivity using host cells containing or engineered to contain ananimalia tRNA splicing endonuclease coupled to a functional readoutsystem. For example, a phenotypic or physiological readout can be usedto assess activity of an animalia tRNA splicing endonuclease in thepresence and absence of the lead compound.

In one embodiment, a phenotypic or physiological readout can be used toassess activity of an animalia tRNA splicing endonuclease in thepresence and absence of the lead compound. For example, the animaliatRNA splicing endonuclease may be overexpressed in a cell in which theanimalia tRNA splicing endonuclease is endogenously expressed. Theeffect of a lead compound can be assayed by measuring the cell growth orviability of the target cell. Such assays can be carried out withrepresentative cells of cell types involved in a particularproliferative disorder. A lower level of proliferation or survival ofthe contacted cells indicates that the lead compound is effective totreat a condition in the patient characterized by uncontrolled cellgrowth. Alternatively, instead of culturing cells from a patient, a leadcompound may be screened using cells of a tumor or malignant cell lineor an endothelial cell line. Specific examples of cell culture modelsinclude, but are not limited to, for lung cancer, primary rat lung tumorcells (Swafford et al., 1997, Mol. Cell. Biol., 17:1366-1374) andlarge-cell undifferentiated cancer cell lines (Mabry et al., 1991,Cancer Cells, 3:53-58); colorectal cell lines for colon cancer (Park andGazdar, 1996, J. Cell Biochem. Suppl. 24:131-141); multiple establishedcell lines for breast cancer (Hambly et al., 1997, Breast Cancer Res.Treat. 43:247-258; Gierthy et al., 1997, Chemosphere 34:1495-1505;Prasad and Church, 1997, Biochem. Biophys. Res. Commun. 232:14-19); anumber of well-characterized cell models for prostate cancer (Webber etal., 1996, Prostate, Part 1, 29:386-394; Part 2, 30:58-64; and Part 3,30:136-142; Boulikas, 1997, Anticancer Res. 17:1471-1505); forgenitourinary cancers, continuous human bladder cancer cell lines(Ribeiro et al., 1997, Int. J. Radiat. Biol. 72:11-20); organ culturesof transitional cell carcinomas (Booth et al., 1997, Lab Invest.76:843-857) and rat progression models (Vet et al., 1997, Biochim.Biophys Acta 1360:39-44); and established cell lines for leukemias andlymphomas (Drexler, 1994, Leuk. Res. 18:919-927, Tohyama, 1997, Int. J.Hematol. 65:309-317). More specific examples of cell lines include thecancer cell line Huh7 (human hepatocellular carcinoma cell line) and thecancer cell line Caco-2 (a colon-cancer cell line). In certainembodiments, the effect of a lead compound on the growth and/orviability of a cancerous cell of a transformed cell is compared to theeffect of such a compound on the growth and/or viability ofnon-cancerous, normal cells. Preferably, compounds that differentiallyaffect the growth and/or viability of cancerous cells or transformedcells are chosen as anti-proliferative agents.

Many assays well-known in the art can be used to assess the survivaland/or growth of a patient cell or cell line following exposure to alead compound; for example, cell proliferation can be assayed bymeasuring Bromodeoxyuridine (BrdU) incorporation (see, e.g., Hoshino etal., 1986, Int. J. Cancer 38, 369; Campana et al., 1988, J. Immunol.Meth. 107:79) or (³H)-thymidine incorporation (see, e.g., Chen, J.,1996, Oncogene 13:1395-403; Jeoung, J., 1995, J. Biol. Chem.270:18367-73), by direct cell count, by detecting changes intranscription, translation or activity of known genes such asproto-oncogenes (e.g., fos, myc) or cell cycle markers (Rb, cdc2, cyclinA, D1, D2, D3, E, etc). The levels of such protein and mRNA and activitycan be determined by any method well known in the art. For example,protein can be quantitated by known immunodiagnostic methods such asWestern blotting or immunoprecipitation using commercially availableantibodies. mRNA can be quantitated using methods that are well knownand routine in the art, for example, using northern analysis, RNaseprotection, the polymerase chain reaction in connection with the reversetranscription. Cell viability can be assessed by using trypan-bluestaining or other cell death or viability markers known in the art. In aspecific embodiment, the level of cellular ATP is measured to determinedcell viability. Differentiation can be assessed, for example, visuallybased on changes in morphology.

The lead compound can also be assessed for its ability to inhibit celltransformation (or progression to malignant phenotype) in vitro. In thisembodiment, cells with a transformed cell phenotype are contacted with alead compound, and examined for change in characteristics associatedwith a transformed phenotype (a set of in vitro characteristicsassociated with a tumorigenic ability in vivo), for example, but notlimited to, colony formation in soft agar, a more rounded cellmorphology, looser substratum attachment, loss of contact inhibition,loss of anchorage dependence, release of proteases such as plasminogenactivator, increased sugar transport, decreased serum requirement, orexpression of fetal antigens, etc. (see Luria et al., 1978, GeneralVirology, 3d Ed., John Wiley & Sons, New York, pp. 436-446).

Loss of invasiveness or decreased adhesion can also be assessed todemonstrate the anti-cancer effects of a lead compound. For example, anaspect of the formation of a metastatic cancer is the ability of aprecancerous or cancerous cell to detach from primary site of diseaseand establish a novel colony of growth at a secondary site. The abilityof a cell to invade peripheral sites reflects its potential for acancerous state. Loss of invasiveness can be measured by a variety oftechniques known in the art including, for example, induction ofE-cadherin-mediated cell-cell adhesion. Such E-cadherin-mediatedadhesion can result in phenotypic reversion and loss of invasiveness(Hordijk et al., 1997, Science 278:1464-66).

Loss of invasiveness can further be examined by inhibition of cellmigration. A variety of 2-dimensional and 3-dimensional cellularmatrices are commercially available (Calbiochem-Novabiochem Corp. SanDiego, Calif.). Cell migration across or into a matrix can be examinedusing microscopy, time-lapsed photography or videography, or by anymethod in the art allowing measurement of cellular migration. In arelated embodiment, loss of invasiveness is examined by response tohepatocyte growth factor (HGF). HGF-induced cell scattering iscorrelated with invasiveness of cells such as Madin-Darby canine kidney(MDCK) cells. This assay identifies a cell population that has lost cellscattering activity in response to HGF (Hordijk et al., 1997, Science278:1464-66).

Alternatively, loss of invasiveness can be measured by cell migrationthrough a chemotaxis chamber (Neuroprobe/Precision Biochemicals Inc.Vancouver, BC). In such assay, a chemo-attractant agent is incubated onone side of the chamber (e.g., the bottom chamber) and cells are platedon a filter separating the opposite side (e.g. the top chamber). Inorder for cells to pass from the top chamber to the bottom chamber, thecells must actively migrate through small pores in the filter.Checkerboard analysis of the number of cells that have migrated can thenbe correlated with invasiveness (see e.g., Ohnishi, T., 1993, Biochem.Biophys. Res. Commun. 193:518-25).

In certain embodiments, a lead compound is tested for its effects, suchas, but not limited to, cytotoxicity, altered gene expression, andaltered morphology, on PBMCs (Peripheral Blood Mononuclear Cells).

4.6.2 Animal Models

The lead compounds identified in the assays described herein can betested for biological activity using animal models for a proliferativedisorder. These include animals engineered to contain an animalia tRNAsplicing endonuclease coupled to a functional readout system, such as atransgenic mouse. Such animal model systems include, but are not limitedto, rats, mice, chicken, cows, monkeys, pigs, dogs, rabbits, etc. In aspecific embodiment of the invention, a compound identified inaccordance with the methods of the invention is tested in a mouse modelsystem. Such model systems are widely used and well-known to the skilledartisan such as the SCID mouse model or transgenic mice.

The anti-angiogenic activity of a compound identified in accordance withthe invention can be determined by using various experimental animalmodels of vascularized tumors. The anti-tumor activity of a compoundidentified in accordance with the invention can be determined byadministering the compound to an animal model and verifying that thecompound is effective in reducing the proliferation or spread of cancercells in said animal model. An example of an animal model for humancancer in general includes, but is not limited to, spontaneouslyoccurring tumors of companion animals (see, e.g., Vail & MacEwen, 2000,Cancer Invest 18(8):781-92).

Examples of animal models for lung cancer include, but are not limitedto, lung cancer animal models described by Zhang & Roth (1994, In Vivo8(5):755-69) and a transgenic mouse model with disrupted p53 function(see, e.g., Morris et al., 1998, J La State Med Soc 150(4):179-85). Anexample of an animal model for breast cancer includes, but is notlimited to, a transgenic mouse that overexpresses cyclin D1 (see, e.g.,Hosokawa et al., 2001, Transgenic Res 10(5):471-8). An example of ananimal model for colon cancer includes, but is not limited to, a TCRbetaand p53 double knockout mouse (see, e.g., Kado et al., 2001, Cancer Res61(6):2395-8). Examples of animal models for pancreatic cancer include,but are not limited to, a metastatic model of Panc02 murine pancreaticadenocarcinoma (see, e.g. Wang et al., 2001, Int J Pancreatol29(1):37-46) and nu-nu mice generated in subcutaneous pancreatic tumours(see, e.g., Ghaneh et al., 2001, Gene Ther 8(3):199-208). Examples ofanimal models for non-Hodgkin's lymphoma include, but are not limitedto, a severe combined immunodeficiency (“SCID”) mouse (see, e.g., Bryantet al., 2000, Lab Invest 80(4):553-73) and an IgHmu-HOX11 transgenicmouse (see, e.g., Hough et al., 1998, Proc Natl Acad Sci USA95(23):13853-8). An example of an animal model for esophageal cancerincludes, but is not limited to, a mouse transgenic for the humanpapillomavirus type 16 E7 oncogene (see, e.g., Herber et al., 1996, JVirol 70(3):1873-81). Examples of animal models for colorectalcarcinomas include, but are not limited to, Apc mouse models (see, e.g.,Fodde & Smits, 2001, Trends Mol Med 7(8):369-73 and Kuraguchi et al.,2000, Oncogene 19(50):5755-63).

The toxicity and/or efficacy of a compound identified in accordance withthe invention can be determined by standard pharmaceutical procedures incell cultures or experimental animals, e.g., for determining the LD₅₀(the dose lethal to 50% of the population) and the ED₅₀ (the dosetherapeutically effective in 50% of the population). Cells and celllines that can be used to assess the cytotoxicity of a compoundidentified in accordance with the invention include, but are not limitedto, peripheral blood mononuclear cells (PBMCs), Caco-2 cells, and Huh7cells. The dose ratio between toxic and therapeutic effects is thetherapeutic index and it can be expressed as the ratio LD₅₀/ED₅₀. Acompound identified in accordance with the invention that exhibits largetherapeutic indices is preferred. While a compound identified inaccordance with the invention that exhibits toxic side effects may beused, care should be taken to design a delivery system that targets suchagents to the site of affected tissue in order to minimize potentialdamage to uninfected cells and, thereby, reduce side effects.

The data obtained from the cell culture assays and animal studies can beused in formulating a range of dosage of a compound identified inaccordance with the invention for use in humans. The dosage of suchagents lies preferably within a range of circulating concentrations thatinclude the ED₅₀ with little or no toxicity. The dosage may vary withinthis range depending upon the dosage form employed and the route ofadministration utilized. For any agent used in the method of theinvention, the therapeutically effective dose can be estimated initiallyfrom cell culture assays. A dose may be formulated in animal models toachieve a circulating plasma concentration range that includes the IC₅₀(ie., the concentration of the compound that achieves a half-maximalinhibition of symptoms) as determined in cell culture. Such informationcan be used to more accurately determine useful doses in humans. Levelsin plasma may be measured, for example, by high performance liquidchromatography.

4.6.3 Design of Congeners or Analogs

The compounds which display the desired biological activity can be usedas lead compounds for the development or design of congeners or analogshaving useful pharmacological activity. For example, once a leadcompound is identified, molecular modeling techniques can be used todesign variants of the compound that can be more effective. Examples ofmolecular modeling systems are the CHARM and QUANTA programs (PolygenCorporation, Waltham, Mass.). CHARM performs the energy minimization andmolecular dynamics functions. QUANTA performs the construction, graphicmodelling and analysis of molecular structure. QUANTA allows interactiveconstruction, modification, visualization, and analysis of the behaviorof molecules with each other.

A number of articles review computer modeling of drugs interactive withspecific proteins, such as Rotivinen et al., 1988, Acta PharmaceuticalFennica 97:159-166; Ripka, 1998, New Scientist 54-57; McKinaly &Rossmann, 1989, Annu. Rev. Pharmacol. Toxiciol. 29: 111-122; Perry &Davies, OSAR: Quantitative Structure-Activity Relationships in DrugDesign pp. 189-193 (Alan R. Liss, Inc. 1989); Lewis & Dean, 1989, Proc.R. Soc. Lond. 236:125-140 and 141-162; Askew et al., 1989, J. Am. Chem.Soc. 111:1082-1090. Other computer programs that screen and graphicallydepict chemicals are available from companies such as BioDesign, Inc.(Pasadena, Calif.), Allelix, Inc. (Mississauga, Ontario, Canada), andHypercube, Inc. (Cambridge, Ontario). Although these are primarilydesigned for application to drugs specific to particular proteins, theycan be adapted to design of drugs specific to any identified region. Theanalogs and congeners can be tested for binding to an animalia tRNAsplicing endonuclease using the above-described screens for biologicactivity. Alternatively, lead compounds with little or no biologicactivity, as ascertained in the screen, can also be used to designanalogs and congeners of the compound that have biologic activity.

4.6.4 Fungal Assays

Various fungal assays can be conducted to determine the specificity of alead compound for an animalia tRNA splicing endonuclease. Any of theassays described above with respect to animalia tRNA splicingendonuclease can be used to assess the effect of a lead comound onfungal tRNA splicing endonuclease. Compounds that affect both animaliatRNA splicing endonuclease and fungal tRNA splicing endonuclease may beused to treat, prevent or ameliorate one or more symptoms of cancerand/or a fungal infection in a cancer patient

4.6.4.1 Fungal Cell-Based Assays with a Labeled Substrate

The FRET cell-based assays may be conducted by microinjecting asubstrate for a fungal tRNA splicing endonuclease into a fungal cell andcontacting the fungal cell with a compound, wherein the substrate islabeled at the 5′ end with a fluorophore and labeled at the 3′ end witha quencher, or alternatively the substrate is labeled at the 5′ end witha quencher and labeled at the 3′ end with a fluorophore, and measuringthe fluorescence of the substrate by, e.g., a fluorescence emissiondetector such as a Viewlux or Analyst. The endogenous tRNA splicingendonuclease will cleave the substrate and result in the production of adetectable fluorescent signal. A compound that inhibits or reduces theactivity of the endogenous tRNA splicing endonuclease will inhibit orreduce the cleavage of the substrate and thus, inhibit or reduce theproduction of a detectable fluorescent signal relative to a negativecontrol (e.g., PBS). A compound that enhances the activity of theendogenous endonuclease will enhance the cleavage of the substrate andthus, increase the production of a detectable fluorescent signalrelative to a negative control (e.g., PBS).

Alternatively, the FRET cell-based assays may be conducted bymicroinjecting a substrate for a fungal tRNA splicing endonuclease intoa fungal cell and contacting the fungal cell with a compound, whereinthe substrate is labeled at the 5′ end with a fluorescent donor moietyand labeled at the 3′ end with a fluorescent acceptor moiety, or thesubstrate is labeled at the 5′ end with a fluorescent acceptor moietyand labeled at the 3′ end with a fluorescent donor moiety, and measuringthe fluorescence of the substrate by, e.g., a fluorescence emissiondetector such as a Viewlux or Analyst. The endogenous tRNA splicingendonuclease will cleave the substrate and result in the production of adetectable fluorescent signal by the fluorescent donor moiety andfluorescent acceptor moiety at the wavelength of the fluorescent donor.A compound that inhibits or reduces the activity of the endogenous tRNAsplicing endonuclease will inhibit or reduce cleavage of the substrateand thus, increase the fluorescence emission of the fluorescent acceptormoiety at the wavelength of the fluorescent donor moiety relative to anegative control (e.g., PBS). A compound that enhances the activity ofthe endogenous tRNA splicing endonuclease will enhance the cleavage ofthe substrate and thus, reduce the fluorescence emission of thefluorescent acceptor moiety at the wavelength of the fluorescent donormoiety relative to a negative control (e.g., PBS). In a preferredembodiment, a negative control (e.g., PBS or another agent that is knownto have no effect on the cleavage of the substrate) and a positivecontrol (e.g., an agent that is known to have an effect on the cleavageof the substrate) are included in the FRET fungal cell-based assaysdescribed herein.

Any nucleotide sequence recognized and excised by a fungal tRNA splicingendonuclease may be utilized as a substrate for a fungal tRNA splicingendonuclease in a FRET assay described herein. For example, a nucleotidesequence comprising a bulge-helix-bulge structure or a mature domain ofa precursor tRNA may be utilized as a substrate for a fungal tRNAsplicing endonuclease in a FRET assay described herein A nucleotidesequence recognized and excised by a fungal tRNA splicing endonucleasemay comprise 10 nucleotides, 15 nucleotides, 20 nucleotides, 25nucleotides, 25 nucleotides, 30 nucleotides, 40 nucleotides, 45nucleotides, 50 nucleotides, 55 nucleotides, 60 nucleotides, 65nucleotides, 75 nucleotides, 100 nucleotides, 125 nucleotides, 150nucleotides, or more. In a specific embodiment, the substrates for atRNA splicing endonuclease utilized in the FRET assays described hereincomprise a tRNA intron. The intron may have a bulge-helix-bulgeconformation. In a preferred embodiment, the nucleotide sequencecomprises a mature domain that contains an intron.

In accordance with the invention, the substrate can be labeled with asingle pair of fluorescent donor and acceptor compounds. The substratecan be labeled with different pairs of fluorescent donor moieties andfluorescent acceptor moieties. For example, two, three, four, five ormore pairs of fluorescent donor moieties and fluorescent acceptormoieties can be used. In this situation, preferably, at least one of thepairs comprise a fluorescent acceptor moiety that has a differentemission spectrum from the fluorescent acceptor moiety of at least oneof the other pairs. Alternatively, when at least three pairs are used,the fluorescent acceptor moiety of the first pair, second pair and thirdpair has a different emission spectrum than the fluorescent acceptormoiety of the other two. Methods for labeling the substrate with afluorescent acceptor moiety, a fluorescent donor moiety and/or quencherare well-known in the art (see, e.g., U.S. Pat. Nos. 6,472,156,6,451,543, 6,348,322, 6,342,379, 6,323,039, 6,297,018, 6,291,201,6,280,981, 5,843,658, and 5,439,797, the disclosures of which areincorporated by reference in their entirety). The labeled substrate canbe microinjected into fungal cells (preferably, yeast) utilizedtechniques well-known to one of skill in the art.

The activity of a compound on a fungal tRNA splicing endonuclease in theFRET cell-based assays can be determined by measuring the fluorescentemission spectra of the substrate utilizing techniques well-known to oneof skill in the art. The fluorescent emission spectra measured depends,in part, on the fluorophore used.

4.6.4.2 Fungal Extract Assays with a Labeled Substrate

The FRET cell-free-based assays may be conducted by contacting asubstrate for a fungal tRNA splicing endonuclease with a fungal extract(e.g., a yeast extract) or a purified fungal tRNA splicing endonucleaseand a compound, wherein the substrate is labeled at the 5′ end with afluorophore and labeled at the 3′ end with a quencher, or alternatively,the substrate is labeled at the 5′ end with a quencher and labeled atthe 3′ end with a fluorophore, and measuring the fluorescence of thesubstrate by, e.g., a fluorescence emission detector such as a Viewluxor Analyst. The tRNA splicing endonuclease will cleave the substrate andresult in the production of a detectable fluorescent signal. A compoundthat inhibits or reduces the activity of the tRNA splicing endonucleasewill inhibit or reduce the cleavage of the substrate and thus, inhibitor reduce the production of a detectable fluorescent signal relative toa negative control (e.g., PBS). A compound that enhances the activity ofthe endogenous endonuclease will enhance the cleavage of the substrateand thus, increase the production of a detectable fluorescent signalrelative to a negative control (e.g., PBS).

Alternatively, the FRET cell-free-based assays may be conducted bycontacting a substrate for a fungal tRNA splicing endonuclease with acell-free extract or a purified fungal tRNA splicing endonuclease and acompound, wherein the substrate is labeled at the 5′ end with afluorescent donor moiety and labeled at the 3′ end with a fluorescentacceptor moiety, or the sbustrate is labeled at the 5′ end with afluorescent acceptor moiety and labeled at the 3′ end with a fluorescentdonor moiety, and measuring the fluorescence of the substrate by, e.g. afluorescence emission detector such as a Viewlux or Analyst. The tRNAsplicing endonuclease in the fungal extract will cleave the substrateand result in the production of a detectable fluorescent signal by thefluorescent donor moiety and fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety. A compound that inhibits orreduces the activity of the endogenous tRNA splicing endonuclease willinhibit or reduce cleavage of the substrate and thus, increase thefluorescence emission of the fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety relative to a negativecontrol (e.g., PBS). A compound that enhances the activity of theendogenous tRNA splicing endonuclease will enhance the cleavage of thesubstrate and thus, reduce the fluorescence emission of the fluorescentacceptor moiety at the wavelength of the fluorescent donor moietyrelative to a negative control (e.g., PBS). In a preferred embodiment, anegative control (e.g., PBS or another agent that is known to have noeffect on the cleavage of the substrate) and a positive control (e.g. anagent that is known to have an effect on the cleavage of the substrate)are included in the FRET fungal extract assays described herein.

In accordance with the invention, the substate can be labeled with asingle pair of fluorescent donor and acceptor moieties. The substratecan be labeled with different pairs of fluorescent donor moieties andfluorescent acceptor moieties. For example, two, three, four, five ormore pairs of fluorescent donor moieties and fluorescent acceptormoieties can be used. In this situation, preferably, at least one of thepairs comprise a fluorescent acceptor moiety that has a differentemission spectrum from the fluorescent acceptor moiety of at least oneof the other pairs. Alternatively, when at least three pairs are used,the fluorescent acceptor moiety of the first pair, second pair and thirdpair has a different emission spectrum than the fluorescent acceptormoiety of the other two. Methods for labeling the substrate with afluorescent acceptor moiety, a fluorescent donor moiety and/or quencherare well-known in the art (see, e.g., U.S. Pat. Nos. 6,472,156,6,451,543, 6,348,322, 6,342,379, 6,323,039, 6,297,018, 6,291,201,6,280,981, 5,843,658, and 5,439,797, the disclosures of which areincorporated by reference in their entirety).

The activity of a compound on a fungal tRNA splicing endonuclease in theFRET fungal extract assays can be determined by measuring thefluorescent emission spectra of the substrate utilizing techniqueswell-known to one of skill in the art. The fluorescent emission spectrameasured depends, in part, on the fluorophore used.

In certain embodiments, an animalia tRNA splicing endonuclease subunitis labeled with a fluorophore and the tRNA substrate is labeled with afluorophore such that binding of the tRNA substrate to the animalia tRNAsplicing endonuclease results in FRET. Compounds can then be assayed fortheir ability to inhibit FRET. If a compound prevents or reduces FRETbetween the labeled substrate and the animalia tRNA splicingendonuclease, the compound is identified as an inhibitor of the animaliatRNA splicing endonuclease-tRNA interaction. This compound can then beassayed for its ability to inhibit the endonuclease activity of theanimalia tRNA splicing endonuclease by any assay well known to theskilled artisan (see, e.g., above).

4.6.4.3 Fungal Cell-Based Assays with Labeled Enzyme

A FRET cell-based assay may be conducted by microinjecting ortransfecting a first subunit of a fungal tRNA splicing endonuclease(e.g., SEN2) labeled with a fluorophore and a second, different subunitof a fungal tRNA splicing endonuclease (e.g., SEN34) labeled with aquencher into a fungal cell and contacting the fungal cell with acompound, and measuring the fluorescence of the fungal tRNA splicingendonuclease by, e.g., a fluorescence emission detector such as aViewlux or Analyst. Preferably, the cell microinjected or transfected isdeficient in one or more of the subunits of the fungal tRNA splicingendonuclease. The formation of the fungal tRNA splicing endonucleasefrom the labeled subunits will result in a reduction in the fluorescencedetectable. A compound that inhibits or reduces the formation of thefungal tRNA splicing endonuclease will enhance the production ofdetectable fluorescent signal relative to a negative control (e.g.,PBS). A compound that enhances the formation of the fungal tRNA splicingendonuclease will reduce or inhibit the fluorescence detectable relativeto a negative control (e.g., PBS).

Alternatively, a FRET cell-based assay may be conducted bymicroinjecting or transfecting a first subunit of a fungal tRNA splicingendonuclease (e.g. SEN2) labeled with a fluorescent donor moiety and asecond, different subunit of a fungal tRNA splicing endonuclease (e.g.,SEN34) labeled with a fluorescent acceptor moiety into a fungal cell andcontacting the fungal cell with a compound, and measuring thefluorescence of the fungal tRNA splicing endonuclease by, e.g., afluorescence emission detector such as a Viewlux or Analyst. Theformation of the fungal tRNA splicing endonuclease will result in theproduction of a detectable fluorescent signal by the fluorescent donormoiety and fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety. A compound that inhibits or reduces theformation of the fungal tRNA splicing endonuclease will reduce thefluorescence emission of the fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety relative to a negativecontrol (e.g., PBS). A compound that enhances the formation of thefungal tRNA splicing endonuclease will increase the fluorescenceemission of the fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety relative to a negative control (e.g. PBS). In apreferred embodiment, a negative control (e.g., PBS or another agentthat is known to have no effect on the cleavage of the substrate) and apositive control (e.g., an agent that is known to have an effect on thecleavage of the substrate) are included in the FRET fungal cell-basedassays described herein.

Methods for labeling a subunit of a fungal tRNA splicing endonucleasewith a fluorescent acceptor moiety, a fluorescent donor moiety and/orquencher are well-known in the art (see, e.g., U.S. Pat. Nos. 6,472,156,6,451,543, 6,348,322, 6,342,379, 6,323,039, 6,297,018, 6,291,201,6,280,981, 5,843,658, and 5,439,797, the disclosures of which areincorporated by reference in their entirety).

4.6.4.4 Other Fungal Assays with Labeled Enzyme

A FRET assay may be conducted by contacting a first subunit of a fungaltRNA splicing endonuclease (e.g., SEN2) labeled with a fluorophore and asecond subunit of a fungal tRNA splicing endonuclease (e.g., SEN34)labeled with a quencher with a compound in vitro under conditionsconducive to the formation of the endonuclease, and measuring thefluorescence of the fungal tRNA splicing endonuclease by, e.g., afluorescence emission detector such as a Viewlux or Analyst. Theformation of the fungal tRNA splicing endonuclease from the labeledsubunits will result in a reduction in the fluorescence detectable. Acompound that inhibits or reduces the formation of the fungal tRNAsplicing endonuclease will enhance the production of detectablefluorescent signal relative to a negative control (e.g., PBS). Acompound that enhances the formation of the fungal tRNA splicingendonuclease will reduce or inhibit the fluorescence detectable relativeto a negative control (e.g., PBS).

Alternatively, a FRET fungal assay may be conducted by contacting afirst subunit of a fungal tRNA splicing endonuclease (e.g., SEN2)labeled with a fluorescent donor moiety and a second, different subunitof a fungal tRNA splicing endonuclease (e.g., SEN34) labeled with afluorescent acceptor moiety with a compound in vitro under conditionsconducive to the formation of the endonuclease, and measuring thefluorescence of the fungal tRNA splicing endonuclease by, e.g., afluorescence emission detector such as a Viewlux or Analyst. Theformation of the fungal tRNA splicing endonuclease will result in theproduction of a detectable fluorescent signal by the fluorescent donormoiety and fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety. A compound that inhibits or reduces theformation of the fungal tRNA splicing endonuclease will reduce thefluorescence emission of the fluorescent acceptor moiety at thewavelength of the fluorescent donor moiety relative to a negativecontrol (e.g., PBS). A compound that enhances the formation of thefungal tRNA splicing endonuclease will increase the fluorescenceemission of the fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety relative to a negative control (e.g., PBS). Ina preferred embodiment, a negative control (e.g., PBS or another agentthat is known to have no effect on the cleavage of the substrate) and apositive control (e.g., an agent that is known to have an effect on thecleavage of the substrate) are included in the FRET fungal assaysdescribed herein.

4.6.4.5 Fluorescence Polarization Assay

The effect of a compound on the activity of an fungal tRNA splicingendonuclease may be determined utilizing a fluorescencepolarization-based assay. In such an assay, a fluorescently labeledsubstrate for a fungal tRNA splicing endonuclease is contacted with anfungal cell-free extract (preferably, a fungal tRNA splicingendonuclease extract) or a purified fungal tRNA splicing endonucleaseand a compound or a member of a library of compounds; and thefluorescently polarized light emitted is measured. An important aspectof this assay is that the size of the substrate used in the assay islarge enough to distinguish a change in fluorescent polarized lightemitted following cleavage of the substrate. The fungal tRNA splicingendonuclease in the cell-free extract or the purified fungal tRNAsplicing endonuclease will cleave the substrate and result in a changein intensity of emitted polarized light. Fluorescently labeledsubstrates when excited with plane polarized light will emit light in afixed plane only if they do not rotate during the period betweenexcitation and emission. The extent of depolarization of the emittedlight depends upon the amount of rotation of the substrate, which isdependent on the size of the substrate. Small substrates rotate morethan larger substrates between the time they are excited and the timethey emit fluorescent light. A small fluorescently labeled substraterotates rapidly and the emitted light is depolarized. A largefluorescently labeled substrate rotates more slowly and results in theemitted light remaining polarized. A compound that inhibits the activityof the fungal tRNA splicing endonuclease will inhibit or reduce thecleavage of the substrate and thus, decrease the rotation of thesubstrate relative to a negative control (e.g., PBS), which will resultin the emitted light remaining polarized. A compound that enhances theactivity of the fungal tRNA splicing endonuclease will enhance thecleavage of the substrate and thus, increase the rotation of thesubstrate relative to a negative control (e.g., PBS), which will resultin more of the emitted light being depolarized.

The light intensities are measured in planes 90° apart and are manytimes designated the horizontal and vertical intensities. In someinstruments the excitation filter is moveable while the emission filteris fixed. In certain other machines the horizontal and verticalintensities are measured simultaneously via fiber optics. Research gradefluorescence polarization instruments are commercially available from,e.g., Pan Vera, BMG Lab Technologies, and LJL Biosystems. Abott providesclinical laboratory instrumentation.

The value of fluorescence polarization is determined by the followingequation:${polarization} = \frac{{intensity}_{vertical} - {intensity}_{horizontal}}{{intensity}_{vertical} + {{intensity}_{horizontal}.}}$

Fluorescence polarization values are most often divided by 1000 andexpressed as millipolarization units (mP).

4.6.4.6 Anti-fungal Assays

The anti-fungal effect of a lead compound can be assessed utilizingtechniques well-known to one of skill in the art. The inventionencompasses methods of anti-fungal susceptibility testing as recommendedby the National Committee for Clinical Laboratories (NCCLS) (SeeNational Committee for Clinical Laboratories Standards. 1995, ProposedStandard M27T. Villanova, Pa., all of which is incorporated herein byreference in its entirety) and other methods known to those skilled inthe art (Pfaller et al., 1993, Infectious Dis. Clin. N. Am. 7: 435-444)The invention encompasses determining anti-fungal activities of the leadcompounds of the invention using macrodilution methods and/ormicrodilution methods using protocols known to those skilled in the art(See, Clancy et al., 1997 Journal of Clinical Microbiology, 35(11):2878-82; Ryder et al., 1998, Antimicrobial Agents and Chemotherapy,42(5):1057-61; U.S. Pat. No. 5,521,153; U.S. Pat. No. 5,883,120, U.S.Pat. No. 5,521,169, all of which are incorporated by reference in theirentirety). Briefly, a fungal strain is cultured in an appropriate liquidmedia, and grown at an appropriate temperature, depending on theparticular fungal strain used for a determined amount of time, which isalso depends on the particular fungal strain used. An innoculum is thenprepared photometrically and the turbidity of the suspension is matchedto that of a standard, e.g., a McFarland standard. The effect of thelead compound on the turbidity of the inoculum is determined visually orspectrophotometrically. The minimal inhibitory concentration of the leadcompound (MIC) is determined, which is defined as the lowestconcentration of the lead compound which prevents visible growth of aninoculum as measured by determining the culture turbidity.

The invention also encompasses colorimetric based assays for determiningthe anti-fungal activity of the lead compounds of the invention. Oneexemplary calorimetric assay for use in the methods of the invention isdescribed by Pfaller et al. (1994, Journal of Clinical Microbiology,32(8): 1993-6, which is incorporated herein by reference in itsentirety; also see Tiballi et al., 1995, Journal of ClinicalMicrobiology, 33(4): 915-7). This assay employs a colorimetric endpointusing an oxidation-reduction indicator (Alamar Biosciences, Inc.,Sacramento Calif.).

The invention encompasses photometric assays for determining theanti-fungal activity of the lead compounds of the invention usingpreviously described methodology (See Clancy et al., 1997 Journal ofClinical Microbiology, 35(11): 2878-82; Jahn et al., 1995, Journal ofClinical Microbiology, 33(3): 661-667 which is incorporated herein byreference in its entirety). This photometric assay is based onquantifying mitochondrial respiration by viable fungi through thereduction of 3-(4,5-dimethyl-2thiazolyl)-2,5,-diphenyl-2H-tetrazoliumbromide (MTT) to formazan. MIC's determined by this assay are defined asthe highest concentration of the lead compound associated with the firstprecipitous drop in optical density. In some embodiments, the compoundsof the invention are assayed for anti-fungal activity usingmacrodilution, microdilution and MTT assays in parallel.

The antifungal properties of the lead compounds of the present inventionmay be determined from a fungal lysis assay, as well as by othermethods, including, inter alia, growth inhibition assays,fluorescence-based fungal viability assays, flow cytometry analyses, andother standard assays known to those skilled in the art. The fungitested in accordance with the invention include, but are not limited tofungi in the genus Blastomyces, including Blastomyces dermatitidis;Paracoccidiodes, including Paracoccidioides brasiliensis; Sporothrix,including Sporothrix schenckii; Cryptococcus; Candida, including Candidaalbicans, Candida tropicalis and Candida glabrala; Aspergillus,including Aspergillus fumigarus and Aspergillus flavus; Histoplasma,including Histoplasma capsulatum; Cryptococcus, including Cryptococcusneoformans; Bipolaris; Cladophialophora; Cladosporium; Drechslera;Exophiala; Fonsecaea; Phialophora; Xylohypha; Ochroconis;Rhinocladiella; Scolecobasidium; and Wangiella.

4.6.5 Mutagenesis Studies

The subunit(s) of an animalia tRNA splicing endonuclease and/or thenucleotide sequence of a substrate for an animalia tRNA splicingendonuclease that are necessary for a compound identified in accordancewith the methods of the invention to modulate the activity of ananimalia tRNA splicing endonuclease can be determined utilizing standardmutagenesis techniques well-known to one of skill in the art. One ormore mutations (e.g., deletions, additions and/or substitutions) may beintroduced into an animalia tRNA splicing endonuclease subunit and theeffect of the mutations on the activity of the animalia tRNA splicingendonuclease in the presence or absence of a compound can be determinedusing an assay described herein. In particular, one or more mutations(e.g., deletions, additions, and/or substitutions) may also beintroduced into a substrate for animalia tRNA endonuclease and theeffect of the mutations on the activity of the animalia tRNA splicingendonuclease in the presence or absence of a compound can be determinedusing an assay described herein. For example, one or more mutations(e.g., deletions, additions and/or substitutions) may be introduced intothe nucleotide sequence for a tRNA intron within the open frame readingof a reporter gene and the effect on the expression of a reporter genein a reporter gene-based assay described herein can be determined. Ifthe mutation in the tRNA intron affects the ability of the compound tomodulate the expression of the reporter gene, then the mutated sequenceplays a role in the activity of the tRNA splicing endonuclease.

Standard techniques known to those of skill in the art can be used tointroduce mutations in the nucleotide sequence of an animalia tRNAsplicing endonuclease and/or the nucleotide sequence of a substrate foran animalia tRNA splicing endonuclease, including, for example,site-directed mutagenesis and PCR-mediated mutagenesis. In a specificembodiment, less than 75 nucleic acid residue substitutions, less than50 nucleic acid residue substitutions, less than 45 nucleic acid residuesubstitutions, less than 40 nucleic acid residue substitutions, lessthan 35 nucleic acid residue substitutions, less than 30 nucleic acidresidue substitutions, less than 25 nucleic acid residue substitutions,less than 20 nucleic acid residue substitutions, less than 15 nucleicacid residue substitutions, less than 10 nucleic acid residuesubstitutions, or less than 5 nucleic acid residue substitutions areintroduced into the nucleotide sequence of an animalia tRNA splicingendonuclease and/or the nucleotide sequence of a substrate for ananimalia tRNA splicing endonuclease.

4.7 Use of Identified Compounds to Treat/Prevent a ProliferativeDisorder

The present invention provides methods of preventing, treating, managingor ameliorating a proliferative disorder or one or more symptomsthereof, said methods comprising administering to a subject in needthereof one or more compounds identified in accordance with the methodsof the invention. In one embodiment, the invention provides a method ofpreventing, treating, managing or ameliorating a proliferative disorderor one or more symptoms thereof, said method comprising administering toa subject in need thereof a dose of a prophylactically ortherapeutically effective amount of one or more compounds identified inaccordance with the methods of the invention. In another embodiment, acompound identified in accordance with the methods of the invention isnot administered to prevent, treat, or ameliorate a proliferativedisorder or one or more symptoms thereof, if such compound has been usedpreviously to prevent, treat, manage or ameliorate said proliferativedisorder.

The invention also provides methods of preventing, treating, managing orameliorating a proliferative disorder or one or more symptoms thereof,said methods comprising administering to a subject in need thereof oneor more of the compounds identified utilizing the screening methodsdescribed herein, and one or more other therapies (e.g., prophylactic ortherapeutic agents), which therapies are currently being used, have beenused or are known to be useful in the prevention, treatment, managementor amelioration of one or more symptoms associated with saidproliferative disorder (including, but not limited to the prophylacticor therapeutic agents listed in Section 4.6.1 hereinbelow). Thetherapies (e.g., prophylactic or therapeutic agents) of the combinationtherapies of the invention can be administered sequentially orconcurrently. In a specific embodiment, the combination therapies of theinvention comprise a compound identified in accordance with theinvention and at least one other therapy that has the same mechanism ofaction as said compound. In another specific embodiment, the combinationtherapies of the invention comprise a compound identified in accordancewith the methods of the invention and at least one other therapy (e.g.,prophylactic or therapeutic agent) which has a different mechanism ofaction than said compound. The combination therapies of the presentinvention improve the prophylactic or therapeutic effect of a compoundof the invention by functioning together with the compound to have anadditive or synergistic effect. The combination therapies of the presentinvention reduce the side effects associated with the therapies (e.g.,prophylactic or therapeutic agents).

The prophylactic or therapeutic agents of the combination therapies canbe administered to a subject in the same pharmaceutical composition.Alternatively, the prophylactic or therapeutic agents of the combinationtherapies can be administered concurrently to a subject in separatepharmaceutical compositions. The prophylactic or therapeutic agents maybe administered to a subject by the same or different routes ofadministration.

In specific embodiment, a pharmaceutical composition comprising one ormore compounds identified in a screening assay described herein isadministered to a subject, preferably a human, to prevent, treat, manageor ameliorate a proliferative disorder or one or more symptoms thereof.In accordance with the invention, the pharmaceutical composition mayalso comprise one or more prophylactic or therapeutic agents which arecurrently being used, have been used or are known to be useful in theprevention, treatment, management or amelioration of a proliferativedisorder or one or more symptoms thereof.

A compound identified in accordance with the methods of the inventionmay be used as a first, second, third, fourth or fifth line of therapyfor a proliferative disorder. The invention provides methods fortreating, managing or ameliorating a proliferative disorder or one ormore symptoms thereof in a subject refractory to conventional therapiesfor such proliferative disorder, said methods comprising administeringto said subject a dose of a prophylactically or therapeuticallyeffective amount of a compound identified in accordance with the methodsof the invention. In particular, a cancer may be determined to berefractory to a therapy means when at least some significant portion ofthe cancer cells are not killed or their cell division arrested inresponse to the therapy. Such a determination can be made either in vivoor in vitro by any method known in the art for assaying theeffectiveness of treatment on cancer cells, using the art-acceptedmeanings of “refractory” in such a context. In a specific embodiment, acancer is refractory where the number of cancer cells has not beensignificantly reduced, or has increased.

The invention provides methods for treating, managing or amelioratingone or more symptoms of a proliferative disorder in a subject refractoryto existing single agent therapies for such proliferative disorder, saidmethods comprising administering to said subject a dose of aprophylactically or therapeutically effective amount of a compoundidentified in accordance with the methods of the invention and a dose ofa prophylactically or therapeutically effective amount of one or moreother therapies (e.g., prophylactic or therapeutic agents). Theinvention also provides methods for treating or managing a proliferativedisorder by administering a compound identified in accordance with themethods of the invention in combination with any other therapy (e.g.,radiation therapy, chemotherapy or surgery) to patients who have provenrefractory to other therapies but are no longer on these therapies. Theinvention also provides methods for the treatment or management of apatient having a proliferative disorder and immunosuppressed by reasonof having previously undergone other therapies. The invention alsoprovides alternative methods for the treatment or management of aproliferative disorder such as cancer where chemotherapy, radiationtherapy, hormonal therapy, and/or biological therapy/immunotherapy hasproven or may prove too toxic, i.e., results in unacceptable orunbearable side effects, for the subject being treated or managed.Further, the invention provides methods for preventing the recurrence ofa proliferative disorder such as cancer in patients that have beentreated and have no disease activity by administering a compoundidentified in accordance with the methods of the invention.

Proliferative disorders that can be treated by the methods encompassedby the invention include, but are not limited to, neoplasms, tumors,metastases, or any disease or disorder characterized by uncontrolledcell growth (e.g., psoriasis and pulmonary fibrosis). The cancer may bea primary or metastatic cancer. Specific examples of cancers that can betreated by the methods encompassed by the invention include, but are notlimited to, cancer of the head, neck, eye, mouth, throat, esophagus,chest, bone, lung, colon, rectum, stomach, prostate, breast, ovaries,kidney, liver, pancreas, and brain. Additional cancers include, but arenot limited to, the following: leukemias such as but not limited to,acute leukemia, acute lymphocytic leukemia, acute myelocytic leukemiassuch as myeloblastic, promyelocytic, myelomonocytic, monocytic,erythroleukemia leukemias and myelodysplastic syndrome, chronicleukemias such as but not limited to, chronic myelocytic (granulocytic)leukemia, chronic lymphocytic leukemia, hairy cell leukemia;polycythemia vera; lymphomas such as but not limited to Hodgkin'sdisease, non-Hodgkin's disease; multiple myelomas such as but notlimited to smoldering multiple myeloma, nonsecretory myeloma,osteosclerotic myeloma, plasma cell leukemia, solitary plasmacytoma andextramedullary plasmacytoma; Waldenström's macroglobulinemia; monoclonalgammopathy of undetermined significance; benign monoclonal gammopathy;heavy chain disease; bone and connective tissue sarcomas such as but notlimited to bone sarcoma, osteosarcoma, chondrosarcoma, Ewing's sarcoma,malignant giant cell tumor, fibrosarcoma of bone, chordoma, periostealsarcoma, soft-tissue sarcomas, angiosarcoma (hemangiosarcoma),fibrosarcoma, Kaposi's sarcoma, leiomyosarcoma, liposarcoma,lymphangiosarcoma, neurilemmoma, rhabdomyosarcoma, synovial sarcoma;brain tumors such as but not limited to, glioma, astrocytoma, brain stemglioma, ependymoma, oligodendroglioma, nonglial tumor, acousticneurinoma, craniopharyngioma, medulloblastoma, meningioma, pineocytoma,pineoblastoma, primary brain lymphoma; breast cancer including but notlimited to adenocarcinoma, lobular (small cell) carcinoma, intraductalcarcinoma, medullary breast cancer, mucinous breast cancer, tubularbreast cancer, papillary breast cancer, Paget's disease, andinflammatory breast cancer; adrenal cancer such as but not limited topheochromocytom and adrenocortical carcinoma; thyroid cancer such as butnot limited to papillary or follicular thyroid cancer, medullary thyroidcancer and anaplastic thyroid cancer; pancreatic cancer such as but notlimited to, insulinoma, gastrinoma, glucagonoma, vipoma,somatostatin-secreting tumor, and carcinoid or islet cell tumor;pituitary cancers such as but limited to Cushing's disease,prolactin-secreting tumor, acromegaly, and diabetes insipius; eyecancers such as but not limited to ocular melanoma such as irismelanoma, choroidal melanoma, and cilliary body melanoma, andretinoblastoma; vaginal cancers such as squamous cell carcinoma,adenocarcinoma, and melanoma; vulvar cancer such as squamous cellcarcinoma, melanoma, adenocarcinoma, basal cell carcinoma, sarcoma, andPaget's disease; cervical cancers such as but not limited to, squamouscell carcinoma, and adenocarcinoma; uterine cancers such as but notlimited to endometrial carcinoma and uterine sarcoma; ovarian cancerssuch as but not limited to, ovarian epithelial carcinoma, borderlinetumor, germ cell tumor, and stromal tumor, esophageal cancers such asbut not limited to, squamous cancer, adenocarcinoma, adenoid cycticcarcinoma, mucoepidermoid carcinoma, adenosquamous carcinoma, sarcoma,melanoma, plasmacytoma, verrucous carcinoma, and oat cell (small cell)carcinoma; stomach cancers such as but not limited to, adenocarcinoma,fungating (polypoid), ulcerating, superficial spreading, diffuselyspreading, malignant lymphoma, liposarcoma, fibrosarcoma, andcarcinosarcoma; colon cancers; rectal cancers; liver cancers such as butnot limited to hepatocellular carcinoma and hepatoblastoma, gallbladdercancers such as adenocarcinoma; cholangiocarcinomas such as but notlimited to pappillary, nodular, and diffuse; lung cancers such asnon-small cell lung cancer, squamous cell carcinoma (epidermoidcarcinoma), adenocarcinoma, large-cell carcinoma and small-cell lungcancer; testicular cancers such as but not limited to germinal tumor,seminoma, anaplastic, classic (typical), spermatocytic, nonseminoma,embryonal carcinoma, teratoma carcinoma, choriocarcinoma (yolk-sactumor), prostate cancers such as but not limited to, adenocarcinoma,leiomyosarcoma, and rhabdomyosarcoma; penal cancers; oral cancers suchas but not limited to squamous cell carcinoma; basal cancers; salivarygland cancers such as but not limited to adenocarcinoma, mucoepidermoidcarcinoma, and adenoidcystic carcinoma; pharynx cancers such as but notlimited to squamous cell cancer, and verrucous; skin cancers such as butnot limited to, basal cell carcinoma, squamous cell carcinoma andmelanoma, superficial spreading melanoma, nodular melanoma, lentigomalignant melanoma, acral lentiginous melanoma; kidney cancers such asbut not limited to renal cell cancer, adenocarcinoma, hypernephroma,fibrosarcoma, transitional cell cancer (renal pelvis and/or uterer);Wilms' tumor; bladder cancers such as but not limited to transitionalcell carcinoma, squamous cell cancer, adenocarcinoma, carcinosarcoma. Inaddition, cancers include myxosarcoma, osteogenic sarcoma,endotheliosarcoma, lymphangioendotheliosarcoma, mesothelioma, synovioma,hemangioblastoma, epithelial carcinoma, cystadenocarcinoma, bronchogeniccarcinoma, sweat gland carcinoma, sebaceous gland carcinoma, papillarycarcinoma and papillary adenocarcinomas (for a review of such disorders,see Fishman et al., 1985, Medicine, 2d Ed., J.B. Lippincott Co.,Philadelphia and Murphy et al., 1997, Informed Decisions: The CompleteBook of Cancer Diagnosis, Treatment, and Recovery, Viking Penguin,Penguin Books U.S.A., Inc., United States of America). It is alsocontemplated that cancers caused by aberrations in apoptosis can also betreated by the methods and compositions of the invention. Such cancersmay include, but not be limited to, follicular lymphomas, carcinomaswith p53 mutations, hormone dependent tumors of the breast, prostate andovary, and precancerous lesions such as familial adenomatous polyposis,and myelodysplastic syndromes.

4.7.1 Other Anti-Cancer Therapies

The present invention provides methods of preventing, treating, managingor ameliorating cancer or one or more symptoms thereof, said methodscomprising administering to a subject in need thereof one or morecompounds identified in accordance with the methods of the invention andone or more therapies (e.g., prophylactic or therapeutic agents).Therapeutic or prophylactic agents include, but are not limited to,peptides, polypeptides, fusion proteins, nucleic acid molecules, smallmolecules, mimetic agents, synthetic drugs, inorganic molecules, andorganic molecules. Any therapy (e.g., chemotherapies, radiationtherapies, hormonal therapies, and/or biologicaltherapies/immunotherapies) which is known to be useful, or which hasbeen used or is currently being used for the prevention, treatment,management or amelioration of cancer or one or more symptoms thereof canbe used in combination with a compound identified in accordance with themethods of the invention. Examples of such agents (i.e., anti-canceragents) include, but are not limited to, angiogenesis inhibitors,topoisomerase inhibitors and immunomodulatory agents (such aschemotherapeutic agents). Angiogenesis inhibitors (i.e., anti-angiogenicagents) include, but are not limited to, angiostatin (plasminogenfragment); antiangiogenic antithrombin III; angiozyme; ABT-627; Bay12-9566; Benefin; Bevacizumab; BMS-275291; cartilage-derived inhibitor(CDI); CAI; CD59 complement fragment; CEP-7055; Col 3; combretastatinA-4; endostatin (collagen XVIII fragment); fibronectin fragment;Gro-beta; Halofuginone; Heparinases; Heparin hexasaccharide fragment;HMV833; human chorionic gonadotropin (hCG); IM-862; Interferonalpha/beta/gamma; Interferon inducible protein (IP-10); Interleukin-12;Kringle 5 (plasminogen fragment); Marirnastat; Metalloproteinaseinhibitors (TIMPs); 2-methoxyestradiol; MMI 270 (CGS 27023A); MoAbIMC-1C11; Neovastat; NM-3; Panzem; PI-88; Placental ribonucleaseinhibitor; plasminogen activator inhibitor; platelet factor-4 (PF4);Prinomastat; Prolactin 16 kD fragment; Proliferin-related protein (PRP);PTK 787/ZK 222594; retinoids; solimastat; squalamine; SS 3304; SU 5416;SU6668; SUl 1248; tetrahydrocortisol-S; tetrathiomolybdate; thalidomide;thrombospondin-1 (TSP-1); TNP-470; transforming growth factor-beta;vasculostatin; vasostatin (calreticulin fragment); ZD6126; ZD 6474;farnesyl transferase inhibitors (FTI); and bisphosphonates. In aspecific embodiment, anti-angiogenic agents do not include antibodies orfragments thereof that immunospecifically bind to integrin α_(v)β₃.

Specific examples of anti-cancer agents which can be used in accordancewith the methods of the invention include, but not limited to: acivicin;aclarubicin; acodazole hydrochloride; acronine; adozelesin; aldesleukin;altretamine; ambomycin; ametantrone acetate; aminoglutethimide;amsacrine; anastrozole; anthramycin; asparaginase; asperlin;azacitidine; azetepa; azotomycin; batimastat; benzodepa; bicalutamide;bisantrene hydrochloride; bisnafide dimesylate; bizelesin; bleomycinsulfate; brequinar sodium; bropirimine; busulfan; cactinomycin;calusterone; caracemide; carbetimer; carboplatin; carmustine; carubicinhydrochloride; carzelesin; cedefingol; chlorambucil; cirolemycin;cisplatin; cladribine; crisnatol mesylate; cyclophosphamide; cytarabine;dacarbazine; dactinomycin; daunorubicin hydrochloride; decitabine;dexormaplatin; dezaguanine; dezaguanine mesylate; diaziquone; docetaxel;doxorubicin; doxorubicin hydrochloride; droloxifene; droloxifenecitrate; dromostanolone propionate; duazomycin; edatrexate; eflornithinehydrochloride; elsamitrucin; enloplatin; enpromate; epipropidine;epirubicin hydrochloride; erbulozole; esorubicin hydrochloride;estramustine; estramustine phosphate sodium; etanidazole; etoposide;etoposide phosphate; etoprine; fadrozole hydrochloride; fazarabine;fenretinide; floxuridine; fludarabine phosphate; fluorouracil;flurocitabine; fosquidone; fostriecin sodium; gemcitabine; gemcitabinehydrochloride; hydroxyurea; idarubicin hydrochloride; ifosfamide;ilmofosine; interleulin II (including recombinant interleukin II, orrIL2), interferon alpha-2a; interferon alpha-2b; interferon alpha-n1;interferon alpha-n3; interferon beta-I a; interferon gamma-I b;iproplatin; irinotecan hydrochloride; lanreotide acetate; letrozole;leuprolide acetate; liarozole hydrochloride; lometrexol sodium;lomustine; losoxantrone hydrochloride; masoprocol; maytansine;mechlorethamine hydrochloride; megestrol acetate; melengestrol acetate;melphalan; menogaril; mercaptopurine; methotrexate; methotrexate sodium;metoprine; meturedepa; mitindomide; mitocarcin; mitocromin; mitogillin;mitomalcin; mitomycin; mitosper; mitotane; mitoxantrone hydrochloride;mycophenolic acid; nocodazole; nogalamycin; ormaplatin; oxisuran;paclitaxel; pegaspargase; peliomycin; pentamustine; peplomycin sulfate;perfosfamide; pipobroman; piposulfan; piroxantrone hydrochloride;plicamycin; plomestane; porfimer sodium; porfiromycin; prednimustine;procarbazine hydrochloride; puromycin; puromycin hydrochloride;pyrazofurin; riboprine; rogletimide; safingol; safingol hydrochloride;semustine; simtrazene; sparfosate sodium; sparsomycin; spirogermaniumhydrochloride; spiromustine; spiroplatin; streptonigrin; streptozocin;sulofenur; talisomycin; tecogalan sodium; tegafur; teloxantronehydrochloride; temoporfin; teniposide; teroxirone; testolactone;thiamiprine; thioguanine; thiotepa; tiazofurin; tirapazamine; toremifenecitrate; trestolone acetate; triciribine phosphate; trimetrexate;trimetrexate glucuronate; triptorelin; tubulozole hydrochloride; uracilmustard; uredepa; vapreotide; verteporfin; vinblastine sulfate;vincristine sulfate; vindesine; vindesine sulfate; vinepidine sulfate;vinglycinate sulfate; vinleurosine sulfate; vinorelbine tartrate;vinrosidine sulfate; vinzolidine sulfate; vorozole; zeniplatin;zinostatin; zorubicin hydrochloride. Other anti-cancer drugs include,but are not limited to: 20-epi-1,25 dihydroxyvitamin D3;5-ethynyluracil; abiraterone; aclarubicin; acylfulvene; adecypenol;adozelesin; aldesleulkin; ALL-TK antagonists; altretamine; ambamustine;amidox; amifostine; aminolevulinic acid; amrubicin; amsacrine;anagrelide; anastrozole; andrographolide; angiogenesis inhibitors;antagonist D; antagonist G; antarelix; anti-dorsalizing morphogeneticprotein-1; antiandrogen, prostatic carcinoma; antiestrogen;antineoplaston; antisense oligonucleotides; aphidicolin glycinate;apoptosis gene modulators; apoptosis regulators; apurinic acid;ara-CDP-DL-PTBA; arginine deaminase; asulacrine; atamestane;atrimustine; axinastatin 1; axinastatin 2; axinastatin 3; azasetron;azatoxin; azatyrosine baccatin III derivatives; balanol; batimastat;BCR/ABL antagonists; benzochlorins; benzoylstaurosporine; beta lactamderivatives; beta-alethine; betaclamycin B; betulinic acid; bFGFinhibitor; bicalutamide; bisantrene; bisaziridinylspermine; bisnafide;bistratene A; bizelesin; breflate; bropirimine; budotitane; buthioninesulfoximine; calcipotriol; calphostin C; camptothecin derivatives;canarypox IL-2; capecitabine; carboxamide-amino-triazole;carboxyamidotriazole; CaRest M3; CARN 700; cartilage derived inhibitor;carzelesin; casein kinase inhibitors (ICOS); castanospermine; cecropinB; cetrorelix; chlorlns; chloroquinoxaline sulfonamide; cicaprost;cis-porphyrin; cladribine; clomifene analogues; clotrimazole;collismycin A; collismycin B; combretastatin A4; combretastatinanalogue; conagenin; crambescidin 816; crisnatol; cryptophycin 8;cryptophycin A derivatives; curacin A; cyclopentanthraquinones;cycloplatam; cypemycin; cytarabine ocfqsfate; cytolytic factor;cytostatin; dacliximab; decitabine; dehydrodidenmin B; deslorelin;dexamethasone; dexifosfamide; dexrazoxane; dexverapamil; diaziquone;didemnin B; didox; diethylnorspermine; dihydro-5-azacytidine;dihydrotaxol, 9-; dioxamycin; diphenyl spiromustine; docetaxel;docosanol; dolasetron; doxifluridine; droloxifene; dronabinol;duocarnycin SA; ebselen; ecomustine; edelfosine; edrecolomab;eflornithine; elemene; emitefur; epirubicin; epristeride; estramustineanalogue; estrogen agonists; estrogen antagonists; etanidazole;etoposide phosphate; exemestane; fadrozole; fazarabine; fenretinide;filgrastim; finasteride; flavopiridol; flezelastine; fluasterone;fludarabine; fluorodaunorunicin hydrochloride; forfenimex; formestane;fostriecin; fotemustine; gadolinium texaphyrin; gallium nitrate;galocitabine; ganirelix; gelatinase inhibitors; gemcitabine; glutathioneinhibitors; hepsulfam; heregulin; hexamethylene bisacetamide; hypericin;ibandronic acid; idarubicin; idoxifene; idramantone; ilmofosine;ilomastat; imidazoacridones; imiquimod; immunostimulant peptides;insuilin-like growth factor-1 receptor inhibitor; interferon agonists;interferons; interleukins; iobenguane; iododoxorubicin; ipomeanol 4-;iroplact; irsogladine; isobengazole; isohomohalicondrin B; itasetron;jasplakinolide; kahalalide F; lamellarin-N triacetate; lanreotide;leinamycin; lenograstim; lentinan sulfate; leptolstatin; letrozole;leukemia inhibiting factor, leukocyte alpha interferon;leuprolide+estrogen+progesterone; leuprorelin; levamisole; liarozole;linear polyamine analogue; lipophilic disaccharide peptide; lipophilicplatinum compounds; lissoclinamide 7; lobaplatin; lombricine;lometrexol; lonidamine; losoxantrone; lovastatin; loxoribine;lurtotecan; lutetium texaphyrin; lysofylline; lytic peptides;maitansine; mannostatin A; marimastat; masoprocol; maspin; matrilysininhibitors; matrix metalloproteinase inhibitors; menogaril; merbarone;meterelin; methioninase; metoclopramide; MIF inhibitor; mifepristone;miltefosine; mirimostim; mismatched double stranded RNA; mitoguazone;mitolactol; mitomycin analogues; mitonafide; mitotoxin fibroblast growthfactor-saporin; mitoxantrone; mofarotene; molgramostim; monoclonalantibody, human chorionic gonadotrophin; monophosphoryl lipidA+myobacterium cell wall sk; mopidamol; multiple drug resistance geneinhibitor; multiple tumor suppressor 1-based therapy; mustard anticanceragent; mycaperoxide B; mycobacterial cell wall extract; myriaporone;N-acetyldinaline; N-substituted benzamides; nafarelin; nagrestip;naloxone+pentazocine; napavin; naphterpin; nartograstim; nedaplatin;nemorubicin; neridronic acid; neutral endopeptidase; nilutamide;nisamycin; nitric oxide modulators; nitroxide antioxidant; nitrullyn;O6-benzylguanine; octreotide; okicenone; oligonucleotides; onapristone;ondansetron; ondansetron; oracin; oral cytokine inducer; ormaplatin;osaterone; oxaliplatin; oxaunomycin; paclitaxel; paclitaxel analogues;paclitaxel derivatives; palauamine; palmitoylrhizoxin; pamidronic acid;panaxytriol; panomifene; parabactin; pazelliptine; pegaspargase;peldesine; pentosan polysulfate sodium; pentostatin; pentrozole;perflubron; perfosfamide; perillyl alcohol; phenazinomycin;phenylacetate; phosphatase inhibitors; picibanil; pilocarpinehydrochloride; pirarubicin; piritrexim; placetin A; placetin B;plasminogen activator inhibitor; platinum complex; platinum compounds;platinum-triamine complex; porfimer sodium; porfiromycin; prednisone;propyl bis-acridone; prostaglandin J2; proteasome inhibitors; proteinA-based immune modulator; protein kinase C inhibitor; protein kinase Cinhibitors, microalgal; protein tyrosine phosphatase inhibitors; purinenucleoside phosphorylase inhibitors; purpurins; pyrazoloacridine;pyridoxylated hemoglobin polyoxyethylene conjugate; raf antagonists;raltitrexed; ramosetron; ras farnesyl protein transferase inhibitors;ras inhibitors; ras-GAP inhibitor; retelliptine demethylated; rhenium Re186 etidronate; rhizoxin; ribozymes; RII retinamide; rogletimide;rohitukine; romurtide; roquinimex; rubiginqne B1; ruboxyl; safingol;saintopin; SarCNU; sarcophytol A; sargramostim; Sdi 1 mimetics;semustine; senescence derived inhibitor 1; sense oligonucleotides;signal transduction inhibitors; signal transduction modulators; singlechain antigen binding protein; sizofuran; sobuzoxane; sodiumborocaptate; sodium phenylacetate; solverol; somatomedin bindingprotein; sonermin; sparfosic acid; spicamycin D; spiromustine;splenopentin; spongistatin 1; squalamine; stem cell inhibitor; stem-celldivision inhibitors; stipiamide; stromelysin inhibitors; sulfinosine;superactive vasoactive intestinal peptide antagonist; suradista;suramin; swainsonine; synthetic glycosaminoglycans; tallimustine;5-fluorouracil; leucovorin; tamoxifen methiodide; tauromustine;tazarotene; tecogalan sodium; tegafur; tellurapyrylium; telomeraseinhibitors; temoporfin; temozolomide; teniposide; tetrachlorodecaoxide;tetrazomine; thaliblastine; thiocoraline; thrombopoietin; thrombopoietinmimetic; thymalfasin; thymopoietin receptor agonist; thymotrinan;thyroid stimulating hormone; tin ethyl etiopurpurin; tirapazamine;titanocene bichloride; topsentin; toremifene; totipotent stem cellfactor; translation inhibitors; tretinoin; triacetyluridine;triciribine; trimetrexate; triptorelin; tropisetron; turosteride;tyrosine kinase inhibitors; tyrphostins; UBC inhibitors; ubenimex;urogenital sinus-derived growth inhibitory factor; urokinase receptorantagonists; vapreotide; variolin B; vector system, erythrocyte genetherapy; thalidomide; velaresol; veramine; verdins; verteporfin;vinorelbine; vinxaltine; vorozole; zanoterone; zeniplatin; zilascorb;and zinostatin stimalamer.

The invention also encompasses the administration of one or morecompounds identified in accordance with the methods of the invention incombination with radiation therapy comprising the use of x-rays, gammarays and other sources of radiation to destroy the cancer cells. Inpreferred embodiments, the radiation treatment is administered asexternal beam radiation or teletherapy wherein the radiation is directedfrom a remote source. In other preferred embodiments, the radiationtreatment is administered as internal therapy or brachytherapy wherein aradiaoactive source is placed inside the body close to cancer cells or atumor mass.

Cancer therapies and their dosages, routes of administration andrecommended usage are known in the art and have been described in suchliterature as the Physician's Desk Reference (56^(th) ed., 2002).

4.8 Compositions and Methods of Administering Compounds

Biologically active compounds identified using the methods of theinvention or a pharmaceutically acceptable salt thereof can beadministered to a patient, preferably a mammal, more preferably a human,suffering from a proliferative disorder. In a specific embodiment, acompound or a pharmaceutically acceptable salt thereof is administeredto a patient, preferably a mammal, more preferably a human, as apreventative measure against a proliferative disorder.

When administered to a patient, the compound or a pharmaceuticallyacceptable salt thereof is preferably administered as component of acomposition that optionally comprises a pharmaceutically acceptablevehicle. The composition can be administered orally, or by any otherconvenient route, for example, by infusion or bolus injection, byabsorption through epithelial or mucocutaneous linings (e.g., oralmucosa, rectal, and intestinal mucosa, etc.) and may be administeredtogether with another biologically active agent. Administration can besystemic or local. Various delivery systems are known, e.g.,encapsulation in liposomes, microparticles, microcapsules, capsules,etc., and can be used to administer the compound and pharmaceuticallyacceptable salts thereof.

Methods of administration include but are not limited to intradermal,intramuscular, intraperitoneal, intravenous, subcutaneous, intranasal,epidural, oral, sublingual, intranasal, intracerebral, intravaginal,transdermal, rectally, by inhalation, or topically, particularly to theears, nose, eyes, or skin. The mode of administration is left to thediscretion of the practitioner. In most instances, administration willresult in the release of the compound or a pharmaceutically acceptablesalt thereof into the bloodstream.

In specific embodiments, it may be desirable to administer the compoundor a pharmaceutically acceptable salt thereof locally. This may beachieved, for example, and not by way of limitation, by local infusionduring surgery, topical application, e.g., in conjunction with a wounddressing after surgery, by injection, by means of a catheter, by meansof a suppository, or by means of an implant, said implant being of aporous, non-porous, or gelatinous material, including membranes, such assialastic membranes, or fibers.

In certain embodiments, it may be desirable to introduce the compound ora pharmaceutically acceptable salt thereof into the central nervoussystem by any suitable route, including intraventricular, intrathecaland epidural injection. Intraventricular injection may be facilitated byan intraventricular catheter, for example, attached to a reservoir, suchas an Ommaya reservoir.

Pulmonary administration can also be employed, e.g., by use of aninhaler or nebulizer, and formulation with an aerosolizing agent, or viaperfusion in a fluorocarbon or synthetic pulmonary surfactant. Incertain embodiments, the compound and pharmaceutically acceptable saltsthereof can be formulated as a suppository, with traditional binders andvehicles such as triglycerides.

In another embodiment, the compound and pharmaceutically acceptablesalts thereof can be delivered in a vesicle, in particular a liposome(see Langer, 1990, Science 249:1527-1533; Treat et al., in Liposomes inthe Therapy of Infectious Disease and Cancer, Lopez-Berestein and Fidler(eds.), Liss, New York, pp. 353-365 (1989); Lopez-Berestein, ibid., pp.317-327; see generally ibid.).

In yet another embodiment, the compound and pharmaceutically acceptablesalts thereof can be delivered in a controlled release system (see,e.g., Goodson, in Medical Applications of Controlled Release, supra,vol. 2, pp. 115-138 (1984)). Other controlled-release systems discussedin the review by Langer, 1990, Science 249:1527-1533 may be used. In oneembodiment, a pump may be used (see Langer, supra; Sefton, 1987, CRCCrit. Ref. Biomed. Eng. 14:201; Buchwald et al., 1980, Surgery 88:507;Saudek et al., 1989, N. Engl. J. Med. 321:574). In another embodiment,polymeric materials can be used (see Medical Applications of ControlledRelease, Langer and Wise (eds.), CRC Pres., Boca Raton, Fla. (1974);Controlled Drug Bioavailability, Drug Product Design and Performance,Smolen and Ball (eds.), Wiley, New York (1984); Ranger and Peppas, 1983,J. Macromol. Sci. Rev. Macromol. Chem. 23:61; see also Levy et al.,1985, Science 228:190; During et al., 1989, Ann. Neurol. 25:351; Howardet al., 1989, J. Neurosurg. 71:105). In yet another embodiment, acontrolled-release system can be placed in proximity of a target RNA ofthe compound or a pharmaceutically acceptable salt thereof, thusrequiring only a fraction of the systemic dose.

Compositions comprising the compound or a pharmaceutically acceptablesalt thereof (“compound compositions”) can additionally comprise asuitable amount of a pharmaceutically acceptable vehicle so as toprovide the form for proper administration to the patient.

In a specific embodiment, the term “pharmaceutically acceptable” meansapproved by a regulatory agency of the Federal or a state government orlisted in the U.S. Pharmacopeia or other generally recognizedpharmacopeia for use in animals, mammals, and more particularly inhumans. The term “vehicle” refers to a diluent, adjuvant, excipient, orcarrier with which a compound of the invention is administered. Suchpharmaceutical vehicles can be liquids, such as water and oils,including those of petroleum, animal, vegetable or synthetic origin,such as peanut oil, soybean oil, mineral oil, sesame oil and the like.The pharmaceutical vehicles can be saline, gum acacia, gelatin, starchpaste, talc, keratin, colloidal silica, urea, and the like. In addition,auxiliary, stabilizing, thickening, lubricating and coloring agents maybe used. When administered to a patient, the pharmaceutically acceptablevehicles are preferably sterile. Water is a preferred vehicle when thecompound of the invention is administered intravenously. Salinesolutions and aqueous dextrose and glycerol solutions can also beemployed as liquid vehicles, particularly for injectable solutions.Suitable pharmaceutical vehicles also include excipients such as starch,glucose, lactose, sucrose, gelatin, malt, rice, flour, chalk, silicagel, sodium stearate, glycerol monostearate, talc, sodium chloride,dried skin milk, glycerol, propylene, glycol, water, ethanol and thelike. Compound compositions, if desired, can also contain minor amountsof wetting or emulsifying agents, or pH buffering agents.

Compound compositions can take the form of solutions, suspensions,emulsion, tablets, pills, pellets, capsules, capsules containingliquids, powders, sustained-release formulations, suppositories,emulsions, aerosols, sprays, suspensions, or any other form suitable foruse. In one embodiment, the pharmaceutically acceptable vehicle is acapsule (see e.g., U.S. Pat. No. 5,698,155). Other examples of suitablepharmaceutical vehicles are described in Remington's PharmaceuticalSciences, Alfonso R. Gennaro, ed., Mack Publishing Co. Easton, Pa., 19thed., 1995, pp. 1447 to 1676, incorporated herein by reference.

In a preferred embodiment, the compound or a pharmaceutically acceptablesalt thereof is formulated in accordance with routine procedures as apharmaceutical composition adapted for oral administration to humanbeings. Compositions for oral delivery may be in the form of tablets,lozenges, aqueous or oily suspensions, granules, powders, emulsions,capsules, syrups, or elixirs, for example. Orally administeredcompositions may contain one or more agents, for example, sweeteningagents such as fructose, aspartame or saccharin; flavoring agents suchas peppermint, oil of wintergreen, or cherry; coloring agents; andpreserving agents, to provide a pharmaceutically palatable preparation.Moreover, where in tablet or pill form, the compositions can be coatedto delay disintegration and absorption in the gastrointestinal tractthereby providing a sustained action over an extended period of time.Selectively permeable membranes surrounding an osmotically activedriving compound are also suitable for orally administered compositions.In these later platforms, fluid from the environment surrounding thecapsule is imbibed by the driving compound, which swells to displace theagent or agent composition through an aperture. These delivery platformscan provide an essentially zero order delivery profile as opposed to thespiked profiles of immediate release formulations. A time delay materialsuch as glycerol monostearate or glycerol stearate may also be used.Oral compositions can include standard vehicles such as mannitol,lactose, starch, magnesium stearate, sodium saccharine, cellulose,magnesium carbonate, and the like. Such vehicles are preferably ofpharmaceutical grade. Typically, compositions for intravenousadministration comprise sterile isotonic aqueous buffer. Wherenecessary, the compositions may also include a solubilizing agent.

In another embodiment, the compound or a pharmaceutically acceptablesalt thereof can be formulated for intravenous administration.Compositions for intravenous administration may optionally include alocal anesthetic such as lignocaine to lessen pain at the site of theinjection. Generally, the ingredients are supplied either separately ormixed together in unit dosage form, for example, as a dry lyophilizedpowder or water-free concentrate in a hermetically sealed container suchas an ampoule or sachette indicating the quantity of active agent. Wherethe compound or a pharmaceutically acceptable salt thereof is to beadministered by infusion, it can be dispensed, for example, with aninfusion bottle containing sterile pharmaceutical grade water or saline.Where the compound or a pharmaceutically acceptable salt thereof isadministered by injection, an ampoule of sterile water for injection orsaline can be provided so that the ingredients may be mixed prior toadministration.

The amount of a compound or a pharmaceutically acceptable salt thereofthat will be effective in the treatment of a particular disease willdepend on the nature of the disease, and can be determined by standardclinical techniques. In addition, in vitro or in vivo assays mayoptionally be employed to help identify optimal dosage ranges. Theprecise dose to be employed will also depend on the route ofadministration, and the seriousness of the disease, and should bedecided according to the judgment of the practitioner and each patient'scircumstances. However, suitable dosage ranges for oral administrationare generally about 0.001 milligram to about 500 milligrams of acompound or a pharmaceutically acceptable salt thereof per kilogram bodyweight per day. In specific preferred embodiments of the invention, theoral dose is about 0.01 milligram to about 100 milligrams per kilogrambody weight per day, more preferably about 0.1 milligram to about 75milligrams per kilogram body weight per day, more preferably about 0.5milligram to 5 milligrams per kilogram body weight per day. The dosageamounts described herein refer to total amounts administered; that is,if more than one compound is administered, or if a compound isadministered with a therapeutic agent, then the preferred dosagescorrespond to the total amount administered. Oral compositionspreferably contain about 10% to about 95% active ingredient by weight.

Suitable dosage ranges for intravenous (i.v.) administration are about0.01 milligram to about 100 milligrams per kilogram body weight per day,about 0.1 milligram to about 35 milligrams per kilogram body weight perday, and about 1 milligram to about 10 milligrams per kilogram bodyweight per day. Suitable dosage ranges for intranasal administration aregenerally about 0.01 pg/kg body weight per day to about 1 mg/kg bodyweight per day. Suppositories generally contain about 0.01 milligram toabout 50 milligrams of a compound of the invention per kilogram bodyweight per day and comprise active ingredient in the range of about 0.5%to about 10% by weight.

Recommended dosages for intradermal, intramuscular, intraperitoneal,subcutaneous, epidural, sublingual, intracerebral, intravaginal,transdermal administration or administration by inhalation are in therange of about 0.001 milligram to about 200 milligrams per kilogram ofbody weight per day. Suitable doses for topical administration are inthe range of about 0.001 milligram to about 1 milligram, depending onthe area of administration. Effective doses may be extrapolated fromdose-response curves derived from in vitro or animal model test systems.Such animal models and systems are well known in the art.

The compound and pharmaceutically acceptable salts thereof arepreferably assayed in vitro and in vivo, for the desired therapeutic orprophylactic activity, prior to use in humans. For example, in vitroassays can be used to determine whether it is preferable to administerthe compound, a pharmaceutically acceptable salt thereof, and/or anothertherapeutic agent. Animal model systems can be used to demonstratesafety and efficacy.

Equivalents:

The present invention is not to be limited in scope by the specificembodiments described herein. Indeed, various modifications of theinvention in addition to those described will become apparent to thoseskilled in the art from the foregoing description and accompanyingfigures. Such modifications are intended to fall within the scope of theappended claims.

Various publications are cited herein, the disclosures of which areincorporated by reference in their entireties.

1. (canceled)
 2. A method for identifying a compound that modulatesanimalia tRNA splicing endonuclease activity, said method comprising:(a) contacting a member of a library of compounds with a cell-freeextract and a nucleic acid comprising a reporter gene, wherein thereporter gene comprises a tRNA intron; and (b) detecting the expressionof said reporter gene, wherein a compound that modulates tRNA splicingendonuclease activity is identified if the expression of said reportergene in the presence of a compound is altered relative to the expressionof said reporter gene in the absence of said compound or the presence ofa control.
 3. A method for identifying a compound that modulatesanimalia tRNA splicing endonuclease activity, said method comprising:(a) contacting a member of a library of compounds with a cell containinga nucleic acid comprising a reporter gene, wherein the reporter genecomprises a tRNA intron; and (b) detecting the expression of saidreporter gene, wherein a compound that modulates tRNA splicingendonuclease activity is identified if the expression of said reportergene in the presence of a compound is altered relative to the expressionof said reporter gene in the absence of said compound or the presence ofa control.
 4. (canceled)
 5. (canceled)
 6. A method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a) contactingan animalia cell containing a substrate of a tRNA splicing endonucleasewith a member of a library of compounds, wherein the substrate islabeled at the 5′ end with a fluorophore and at the 3′ end with aquencher; and (b) measuring the activity of the tRNA splicingendonuclease, wherein an antiproliferative compound that inhibits orreduces tRNA splicing activity is identified if a fluorescent signal isnot detectable or decreased in the presence of the compound relative tothe absence of the compound or the presence of a control.
 7. (canceled)8. (canceled)
 9. A method of identifying an antiproliferative compoundthat inhibits or reduces animalia tRNA splicing endonuclease activity,said method comprising: (a) contacting an animalia cell containingsubstrate of a tRNA splicing endonuclease with a member of a library ofcompounds, wherein said substrate is labeled at the 5′ end with afluorescent donor moiety and labeled at the 3′ end with a fluorescentacceptor moiety; and (b) measuring the activity of the tRNA splicingendonuclease, wherein an antiproliferative compound that inhibits orreduces tRNA splicing activity is identified if the fluorescenceemission of the fluorescent acceptor moiety at the wavelength of thefluorescent donor moiety in the presence of the compound is increasedrelative to the absence of the compound or the presence of a control.10. A method of identifying an antiproliferative compound that inhibitsor reduces animalia tRNA splicing endonuclease activity, said methodcomprising: (a) contacting an animalia cell-free extract with asubstrate of a tRNA splicing endonuclease and a member of a library ofcompounds, wherein the substrate is labeled at the 5′ end with afluorophore and at the 3′ end with a quencher; and (b) measuring theactivity of the tRNA splicing endonuclease, wherein an antiproliferativecompound that inhibits or reduces tRNA splicing activity is identifiedif a fluorescent signal is not detectable or decreased in the presenceof the compound is decreased relative to the absence of the compound orthe presence of a control.
 11. A method of identifying anantiproliferative compound that inhibits or reduces animalia tRNAsplicing endonuclease activity, said method comprising: (a) contactingan animalia cell-free extract with a substrate of a tRNA splicingendonuclease and a member of a library of compounds, wherein saidsubstrate is labeled at the 5′ end with a fluorescent donor moiety andlabeled at the 3′ end with a fluorescent acceptor moiety; and (b)measuring the activity of the tRNA splicing endonuclease, wherein anantiproliferative compound that inhibits or reduces tRNA splicingactivity is identified if the fluorescence emission of the fluorescentacceptor moiety at the wavelength of the fluorescent donor moiety in thepresence of the compound is increased relative to the absence of thecompound or the presence of a control.
 12. The method of claim 2 or 3,wherein the compound inhibits tRNA splicing endonuclease activity. 13.The method of claim 2 or 3, wherein the compound enhances tRNA splicingendonuclease activity.
 14. The method of any one of claims 2, 3, 6, 9,10 and 11, wherein the method further comprises determining thestructure of the compound that modulates tRNA splicing endonucleaseactivity.
 15. The method of claim 2, or 3, wherein the reporter geneencodes firefly luciferase, renilla luciferase, click beetle luciferase,green fluorescent protein, yellow fluorescent protein, red fluorescentprotein, cyan fluorescent protein, blue fluorescent protein,beta-galactosidase, beta-glucoronidase, beta-lactamase, chloramphenicolacetyltransferase, or alkaline phosphatase.
 16. The method of claim 2 or3, wherein the cell is selected from the group consisting of 293T, HeLa,MCF7, Wi-38, SkBr3, Jurkat, CEM, THP1, 3T3, and Raw264.7 cells.
 17. Themethod of claim 2, 10 or 11, wherein the cell-free extract is a cellextract.
 18. The method of any one of claims 2, 3, 6, 9, 10 and 11wherein the compound is selected from a combinatorial library ofcompounds comprising peptoids; random biooligomers; diversomers such ashydantoins, benzodiazepines and dipeptides; vinylogous polypeptides;nonpeptidal peptidomimetics; oligocarbamates; peptidyl phosphonates;peptide nucleic acid libraries; antibody libraries; carbohydratelibraries; and small organic molecule libraries.
 19. The method of claim18, wherein the small organic molecule libraries are libraries ofbenzodiazepines, isoprenoids, thiazolidinones, metathiazanones,pyrrolidines, morpholino compounds, or diazepindiones.
 20. The method ofclaim 2 or 3, wherein the step of contacting a library of compounds witha cell is in an aqueous solution comprising a buffer and a combinationof salts.
 21. The method of claim 20, wherein the aqueous solutionapproximates or mimics physiologic conditions.
 22. The method of claim20, wherein the aqueous solution further comprises a detergent or asurfactant.
 23. The method of claim 14, wherein the structure of thecompound is determined by mass spectroscopy, NMR, vibrationalspectroscopy, or X-ray crystallography.
 24. The method of any one ofclaims 2, 3, 6, 9, 10 and 11, wherein the compound directly binds thetRNA splicing endonuclease.
 25. The method of claim 2 or 3, wherein thecompound binds to an RNA transcribed from said reporter gene.
 26. Themethod of claim 6, 9, 10 or 11, wherein the compound binds to thesubstrate.
 27. The method of claim 2 or 3, wherein the compound bindsthe tRNA intron.
 28. The method of any one of claims 2, 3, 6, 9, 10 and11, wherein the compound disrupts an interaction between the tRNA andthe tRNA splicing endonuclease.
 29. The method of claim 2 or 3, whereinthe compound disrupts an interaction between the tRNA intron and thetRNA splicing endonuclease.
 30. The method of claim 2 or 3, wherein saidcell is stably transfected with said nucleic acid.
 31. The method ofclaim 2 or 3, wherein said cell is transiently transfected with saidnucleic acid.
 32. The method of claim 2 or 3, wherein said cell istransfected with an episomal expression vector comprising said nucleicacid. 33-39. (canceled)
 40. A method of identifying a therapeutic agentfor the treatment or prevention of cancer, or amelioration of a symptomthereof, said method comprising: (a) contacting a member of a library ofcompounds with a cell containing a nucleic acid comprising a reportergene, wherein the reporter gene comprises a tRNA intron; and (b)detecting the expression of said reporter gene, wherein if a compoundthat reduces the expression of said reporter gene relative to theexpression of said reporter gene in the absence of said compound or thepresence of a control is detected in (b), then (c) contacting thecompound with a cancer cell or a neoplastic cell and detecting theproliferation of said cancer cell or neoplastic cell, so that if thecompound reduces or inhibits the proliferation of the cancer cell orneoplastic cell, the compound is identified as an antiproliferativecompound.
 41. The method of claim 40 further comprising (d) testing saidcompound in an animal model for cancer, wherein said testing comprisesadministering said compound to said animal model and verifying that thecompound is effective in reducing the proliferation or spread of cancercells in said animal model. 42-44. (canceled)
 45. The method of claim 6,9, 10 or 11 wherein the substrate comprises a mature domain.
 46. Themethod of claim 2 or 3, wherein said method further comprises: (d)determining the cytotoxic activity of the compound.
 47. The method ofclaim 2, 3, 6, 9, 10 or 11, wherein said method further comprises: (c)determining the cytotoxic activity of the compound.
 48. The method ofclaim 2 or 3, wherein said method further comprises: (d) determining thecytostatic activity of the compound.
 49. The method of claim 2, 3, 6, 9,10 or 11, wherein said method further comprises: (c) determining thecytostatic activity of the compound.
 50. The method of claim 2 or 3,wherein said method further comprises: (d) measuring the effect of thecompound on yeast tRNA splicing endonuclease.
 51. The method of claim 2,3, 6, 9, 10 or 11, wherein said method further comprises: (c) measuringthe effect of the compound on yeast tRNA splicing endonuclease. 52-54.(canceled)